mm/huge_memory.c

   1 /*
   2  *  Copyright (C) 2009  Red Hat, Inc.
   3  *
   4  *  This work is licensed under the terms of the GNU GPL, version 2. See
   5  *  the COPYING file in the top-level directory.
   6  */
   7
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10 #include <linux/mm.h>
  11 #include <linux/sched.h>
  12 #include <linux/highmem.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/mmu_notifier.h>
  15 #include <linux/rmap.h>
  16 #include <linux/swap.h>
  17 #include <linux/shrinker.h>
  18 #include <linux/mm_inline.h>
  19 #include <linux/dax.h>
  20 #include <linux/kthread.h>
  21 #include <linux/khugepaged.h>
  22 #include <linux/freezer.h>
  23 #include <linux/mman.h>
  24 #include <linux/pagemap.h>
  25 #include <linux/migrate.h>
  26 #include <linux/hashtable.h>
  27 #include <linux/userfaultfd_k.h>
  28
  29 #include <asm/tlb.h>
  30 #include <asm/pgalloc.h>
  31 #include "internal.h"
  32
  33 /*
  34  * By default transparent hugepage support is disabled in order that avoid
  35  * to risk increase the memory footprint of applications without a guaranteed
  36  * benefit. When transparent hugepage support is enabled, is for all mappings,
  37  * and khugepaged scans all mappings.
  38  * Defrag is invoked by khugepaged hugepage allocations and by page faults
  39  * for all hugepage allocations.
  40  */
  41 unsigned long transparent_hugepage_flags __read_mostly =
  42 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
  43         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
  44 #endif
  45 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
  46         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
  47 #endif
  48         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
  49         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
  50         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
  51
  52 /* default scan 8*512 pte (or vmas) every 30 second */
  53 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
  54 static unsigned int khugepaged_pages_collapsed;
  55 static unsigned int khugepaged_full_scans;
  56 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
  57 /* during fragmentation poll the hugepage allocator once every minute */
  58 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
  59 static struct task_struct *khugepaged_thread __read_mostly;
  60 static DEFINE_MUTEX(khugepaged_mutex);
  61 static DEFINE_SPINLOCK(khugepaged_mm_lock);
  62 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
  63 /*
  64  * default collapse hugepages if there is at least one pte mapped like
  65  * it would have happened if the vma was large enough during page
  66  * fault.
  67  */
  68 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
  69
  70 static int khugepaged(void *none);
  71 static int khugepaged_slab_init(void);
  72 static void khugepaged_slab_exit(void);
  73
  74 #define MM_SLOTS_HASH_BITS 10
  75 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
  76
  77 static struct kmem_cache *mm_slot_cache __read_mostly;
  78
  79 /**
  80  * struct mm_slot - hash lookup from mm to mm_slot
  81  * @hash: hash collision list
  82  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
  83  * @mm: the mm that this information is valid for
  84  */
  85 struct mm_slot {
  86         struct hlist_node hash;
  87         struct list_head mm_node;
  88         struct mm_struct *mm;
  89 };
  90
  91 /**
  92  * struct khugepaged_scan - cursor for scanning
  93  * @mm_head: the head of the mm list to scan
  94  * @mm_slot: the current mm_slot we are scanning
  95  * @address: the next address inside that to be scanned
  96  *
  97  * There is only the one khugepaged_scan instance of this cursor structure.
  98  */
  99 struct khugepaged_scan {
 100         struct list_head mm_head;
 101         struct mm_slot *mm_slot;
 102         unsigned long address;
 103 };
 104 static struct khugepaged_scan khugepaged_scan = {
 105         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
 106 };
 107
 108
 109 static int set_recommended_min_free_kbytes(void)
 110 {
 111         struct zone *zone;
 112         int nr_zones = 0;
 113         unsigned long recommended_min;
 114
 115         for_each_populated_zone(zone)
 116                 nr_zones++;
 117
 118         /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
 119         recommended_min = pageblock_nr_pages * nr_zones * 2;
 120
 121         /*
 122          * Make sure that on average at least two pageblocks are almost free
 123          * of another type, one for a migratetype to fall back to and a
 124          * second to avoid subsequent fallbacks of other types There are 3
 125          * MIGRATE_TYPES we care about.
 126          */
 127         recommended_min += pageblock_nr_pages * nr_zones *
 128                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
 129
 130         /* don't ever allow to reserve more than 5% of the lowmem */
 131         recommended_min = min(recommended_min,
 132                               (unsigned long) nr_free_buffer_pages() / 20);
 133         recommended_min <<= (PAGE_SHIFT-10);
 134
 135         if (recommended_min > min_free_kbytes) {
 136                 if (user_min_free_kbytes >= 0)
 137                         pr_info("raising min_free_kbytes from %d to %lu "
 138                                 "to help transparent hugepage allocations\n",
 139                                 min_free_kbytes, recommended_min);
 140
 141                 min_free_kbytes = recommended_min;
 142         }
 143         setup_per_zone_wmarks();
 144         return 0;
 145 }
 146
 147 static int start_stop_khugepaged(void)
 148 {
 149         int err = 0;
 150         if (khugepaged_enabled()) {
 151                 if (!khugepaged_thread)
 152                         khugepaged_thread = kthread_run(khugepaged, NULL,
 153                                                         "khugepaged");
 154                 if (unlikely(IS_ERR(khugepaged_thread))) {
 155                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
 156                         err = PTR_ERR(khugepaged_thread);
 157                         khugepaged_thread = NULL;
 158                         goto fail;
 159                 }
 160
 161                 if (!list_empty(&khugepaged_scan.mm_head))
 162                         wake_up_interruptible(&khugepaged_wait);
 163
 164                 set_recommended_min_free_kbytes();
 165         } else if (khugepaged_thread) {
 166                 kthread_stop(khugepaged_thread);
 167                 khugepaged_thread = NULL;
 168         }
 169 fail:
 170         return err;
 171 }
 172
 173 static atomic_t huge_zero_refcount;
 174 struct page *huge_zero_page __read_mostly;
 175
 176 struct page *get_huge_zero_page(void)
 177 {
 178         struct page *zero_page;
 179 retry:
 180         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 181                 return READ_ONCE(huge_zero_page);
 182
 183         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 184                         HPAGE_PMD_ORDER);
 185         if (!zero_page) {
 186                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 187                 return NULL;
 188         }
 189         count_vm_event(THP_ZERO_PAGE_ALLOC);
 190         preempt_disable();
 191         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 192                 preempt_enable();
 193                 __free_pages(zero_page, compound_order(zero_page));
 194                 goto retry;
 195         }
 196
 197         /* We take additional reference here. It will be put back by shrinker */
 198         atomic_set(&huge_zero_refcount, 2);
 199         preempt_enable();
 200         return READ_ONCE(huge_zero_page);
 201 }
 202
 203 static void put_huge_zero_page(void)
 204 {
 205         /*
 206          * Counter should never go to zero here. Only shrinker can put
 207          * last reference.
 208          */
 209         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 210 }
 211
 212 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
 213                                         struct shrink_control *sc)
 214 {
 215         /* we can free zero page only if last reference remains */
 216         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
 217 }
 218
 219 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 220                                        struct shrink_control *sc)
 221 {
 222         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
 223                 struct page *zero_page = xchg(&huge_zero_page, NULL);
 224                 BUG_ON(zero_page == NULL);
 225                 __free_pages(zero_page, compound_order(zero_page));
 226                 return HPAGE_PMD_NR;
 227         }
 228
 229         return 0;
 230 }
 231
 232 static struct shrinker huge_zero_page_shrinker = {
 233         .count_objects = shrink_huge_zero_page_count,
 234         .scan_objects = shrink_huge_zero_page_scan,
 235         .seeks = DEFAULT_SEEKS,
 236 };
 237
 238 #ifdef CONFIG_SYSFS
 239
 240 static ssize_t double_flag_show(struct kobject *kobj,
 241                                 struct kobj_attribute *attr, char *buf,
 242                                 enum transparent_hugepage_flag enabled,
 243                                 enum transparent_hugepage_flag req_madv)
 244 {
 245         if (test_bit(enabled, &transparent_hugepage_flags)) {
 246                 VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
 247                 return sprintf(buf, "[always] madvise never\n");
 248         } else if (test_bit(req_madv, &transparent_hugepage_flags))
 249                 return sprintf(buf, "always [madvise] never\n");
 250         else
 251                 return sprintf(buf, "always madvise [never]\n");
 252 }
 253 static ssize_t double_flag_store(struct kobject *kobj,
 254                                  struct kobj_attribute *attr,
 255                                  const char *buf, size_t count,
 256                                  enum transparent_hugepage_flag enabled,
 257                                  enum transparent_hugepage_flag req_madv)
 258 {
 259         if (!memcmp("always", buf,
 260                     min(sizeof("always")-1, count))) {
 261                 set_bit(enabled, &transparent_hugepage_flags);
 262                 clear_bit(req_madv, &transparent_hugepage_flags);
 263         } else if (!memcmp("madvise", buf,
 264                            min(sizeof("madvise")-1, count))) {
 265                 clear_bit(enabled, &transparent_hugepage_flags);
 266                 set_bit(req_madv, &transparent_hugepage_flags);
 267         } else if (!memcmp("never", buf,
 268                            min(sizeof("never")-1, count))) {
 269                 clear_bit(enabled, &transparent_hugepage_flags);
 270                 clear_bit(req_madv, &transparent_hugepage_flags);
 271         } else
 272                 return -EINVAL;
 273
 274         return count;
 275 }
 276
 277 static ssize_t enabled_show(struct kobject *kobj,
 278                             struct kobj_attribute *attr, char *buf)
 279 {
 280         return double_flag_show(kobj, attr, buf,
 281                                 TRANSPARENT_HUGEPAGE_FLAG,
 282                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 283 }
 284 static ssize_t enabled_store(struct kobject *kobj,
 285                              struct kobj_attribute *attr,
 286                              const char *buf, size_t count)
 287 {
 288         ssize_t ret;
 289
 290         ret = double_flag_store(kobj, attr, buf, count,
 291                                 TRANSPARENT_HUGEPAGE_FLAG,
 292                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 293
 294         if (ret > 0) {
 295                 int err;
 296
 297                 mutex_lock(&khugepaged_mutex);
 298                 err = start_stop_khugepaged();
 299                 mutex_unlock(&khugepaged_mutex);
 300
 301                 if (err)
 302                         ret = err;
 303         }
 304
 305         return ret;
 306 }
 307 static struct kobj_attribute enabled_attr =
 308         __ATTR(enabled, 0644, enabled_show, enabled_store);
 309
 310 static ssize_t single_flag_show(struct kobject *kobj,
 311                                 struct kobj_attribute *attr, char *buf,
 312                                 enum transparent_hugepage_flag flag)
 313 {
 314         return sprintf(buf, "%d\n",
 315                        !!test_bit(flag, &transparent_hugepage_flags));
 316 }
 317
 318 static ssize_t single_flag_store(struct kobject *kobj,
 319                                  struct kobj_attribute *attr,
 320                                  const char *buf, size_t count,
 321                                  enum transparent_hugepage_flag flag)
 322 {
 323         unsigned long value;
 324         int ret;
 325
 326         ret = kstrtoul(buf, 10, &value);
 327         if (ret < 0)
 328                 return ret;
 329         if (value > 1)
 330                 return -EINVAL;
 331
 332         if (value)
 333                 set_bit(flag, &transparent_hugepage_flags);
 334         else
 335                 clear_bit(flag, &transparent_hugepage_flags);
 336
 337         return count;
 338 }
 339
 340 /*
 341  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
 342  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
 343  * memory just to allocate one more hugepage.
 344  */
 345 static ssize_t defrag_show(struct kobject *kobj,
 346                            struct kobj_attribute *attr, char *buf)
 347 {
 348         return double_flag_show(kobj, attr, buf,
 349                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 350                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 351 }
 352 static ssize_t defrag_store(struct kobject *kobj,
 353                             struct kobj_attribute *attr,
 354                             const char *buf, size_t count)
 355 {
 356         return double_flag_store(kobj, attr, buf, count,
 357                                  TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
 358                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
 359 }
 360 static struct kobj_attribute defrag_attr =
 361         __ATTR(defrag, 0644, defrag_show, defrag_store);
 362
 363 static ssize_t use_zero_page_show(struct kobject *kobj,
 364                 struct kobj_attribute *attr, char *buf)
 365 {
 366         return single_flag_show(kobj, attr, buf,
 367                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 368 }
 369 static ssize_t use_zero_page_store(struct kobject *kobj,
 370                 struct kobj_attribute *attr, const char *buf, size_t count)
 371 {
 372         return single_flag_store(kobj, attr, buf, count,
 373                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 374 }
 375 static struct kobj_attribute use_zero_page_attr =
 376         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
 377 #ifdef CONFIG_DEBUG_VM
 378 static ssize_t debug_cow_show(struct kobject *kobj,
 379                                 struct kobj_attribute *attr, char *buf)
 380 {
 381         return single_flag_show(kobj, attr, buf,
 382                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 383 }
 384 static ssize_t debug_cow_store(struct kobject *kobj,
 385                                struct kobj_attribute *attr,
 386                                const char *buf, size_t count)
 387 {
 388         return single_flag_store(kobj, attr, buf, count,
 389                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
 390 }
 391 static struct kobj_attribute debug_cow_attr =
 392         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
 393 #endif /* CONFIG_DEBUG_VM */
 394
 395 static struct attribute *hugepage_attr[] = {
 396         &enabled_attr.attr,
 397         &defrag_attr.attr,
 398         &use_zero_page_attr.attr,
 399 #ifdef CONFIG_DEBUG_VM
 400         &debug_cow_attr.attr,
 401 #endif
 402         NULL,
 403 };
 404
 405 static struct attribute_group hugepage_attr_group = {
 406         .attrs = hugepage_attr,
 407 };
 408
 409 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
 410                                          struct kobj_attribute *attr,
 411                                          char *buf)
 412 {
 413         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
 414 }
 415
 416 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
 417                                           struct kobj_attribute *attr,
 418                                           const char *buf, size_t count)
 419 {
 420         unsigned long msecs;
 421         int err;
 422
 423         err = kstrtoul(buf, 10, &msecs);
 424         if (err || msecs > UINT_MAX)
 425                 return -EINVAL;
 426
 427         khugepaged_scan_sleep_millisecs = msecs;
 428         wake_up_interruptible(&khugepaged_wait);
 429
 430         return count;
 431 }
 432 static struct kobj_attribute scan_sleep_millisecs_attr =
 433         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
 434                scan_sleep_millisecs_store);
 435
 436 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
 437                                           struct kobj_attribute *attr,
 438                                           char *buf)
 439 {
 440         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
 441 }
 442
 443 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
 444                                            struct kobj_attribute *attr,
 445                                            const char *buf, size_t count)
 446 {
 447         unsigned long msecs;
 448         int err;
 449
 450         err = kstrtoul(buf, 10, &msecs);
 451         if (err || msecs > UINT_MAX)
 452                 return -EINVAL;
 453
 454         khugepaged_alloc_sleep_millisecs = msecs;
 455         wake_up_interruptible(&khugepaged_wait);
 456
 457         return count;
 458 }
 459 static struct kobj_attribute alloc_sleep_millisecs_attr =
 460         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
 461                alloc_sleep_millisecs_store);
 462
 463 static ssize_t pages_to_scan_show(struct kobject *kobj,
 464                                   struct kobj_attribute *attr,
 465                                   char *buf)
 466 {
 467         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
 468 }
 469 static ssize_t pages_to_scan_store(struct kobject *kobj,
 470                                    struct kobj_attribute *attr,
 471                                    const char *buf, size_t count)
 472 {
 473         int err;
 474         unsigned long pages;
 475
 476         err = kstrtoul(buf, 10, &pages);
 477         if (err || !pages || pages > UINT_MAX)
 478                 return -EINVAL;
 479
 480         khugepaged_pages_to_scan = pages;
 481
 482         return count;
 483 }
 484 static struct kobj_attribute pages_to_scan_attr =
 485         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
 486                pages_to_scan_store);
 487
 488 static ssize_t pages_collapsed_show(struct kobject *kobj,
 489                                     struct kobj_attribute *attr,
 490                                     char *buf)
 491 {
 492         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
 493 }
 494 static struct kobj_attribute pages_collapsed_attr =
 495         __ATTR_RO(pages_collapsed);
 496
 497 static ssize_t full_scans_show(struct kobject *kobj,
 498                                struct kobj_attribute *attr,
 499                                char *buf)
 500 {
 501         return sprintf(buf, "%u\n", khugepaged_full_scans);
 502 }
 503 static struct kobj_attribute full_scans_attr =
 504         __ATTR_RO(full_scans);
 505
 506 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
 507                                       struct kobj_attribute *attr, char *buf)
 508 {
 509         return single_flag_show(kobj, attr, buf,
 510                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 511 }
 512 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
 513                                        struct kobj_attribute *attr,
 514                                        const char *buf, size_t count)
 515 {
 516         return single_flag_store(kobj, attr, buf, count,
 517                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
 518 }
 519 static struct kobj_attribute khugepaged_defrag_attr =
 520         __ATTR(defrag, 0644, khugepaged_defrag_show,
 521                khugepaged_defrag_store);
 522
 523 /*
 524  * max_ptes_none controls if khugepaged should collapse hugepages over
 525  * any unmapped ptes in turn potentially increasing the memory
 526  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 527  * reduce the available free memory in the system as it
 528  * runs. Increasing max_ptes_none will instead potentially reduce the
 529  * free memory in the system during the khugepaged scan.
 530  */
 531 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
 532                                              struct kobj_attribute *attr,
 533                                              char *buf)
 534 {
 535         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
 536 }
 537 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
 538                                               struct kobj_attribute *attr,
 539                                               const char *buf, size_t count)
 540 {
 541         int err;
 542         unsigned long max_ptes_none;
 543
 544         err = kstrtoul(buf, 10, &max_ptes_none);
 545         if (err || max_ptes_none > HPAGE_PMD_NR-1)
 546                 return -EINVAL;
 547
 548         khugepaged_max_ptes_none = max_ptes_none;
 549
 550         return count;
 551 }
 552 static struct kobj_attribute khugepaged_max_ptes_none_attr =
 553         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
 554                khugepaged_max_ptes_none_store);
 555
 556 static struct attribute *khugepaged_attr[] = {
 557         &khugepaged_defrag_attr.attr,
 558         &khugepaged_max_ptes_none_attr.attr,
 559         &pages_to_scan_attr.attr,
 560         &pages_collapsed_attr.attr,
 561         &full_scans_attr.attr,
 562         &scan_sleep_millisecs_attr.attr,
 563         &alloc_sleep_millisecs_attr.attr,
 564         NULL,
 565 };
 566
 567 static struct attribute_group khugepaged_attr_group = {
 568         .attrs = khugepaged_attr,
 569         .name = "khugepaged",
 570 };
 571
 572 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
 573 {
 574         int err;
 575
 576         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
 577         if (unlikely(!*hugepage_kobj)) {
 578                 pr_err("failed to create transparent hugepage kobject\n");
 579                 return -ENOMEM;
 580         }
 581
 582         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
 583         if (err) {
 584                 pr_err("failed to register transparent hugepage group\n");
 585                 goto delete_obj;
 586         }
 587
 588         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
 589         if (err) {
 590                 pr_err("failed to register transparent hugepage group\n");
 591                 goto remove_hp_group;
 592         }
 593
 594         return 0;
 595
 596 remove_hp_group:
 597         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
 598 delete_obj:
 599         kobject_put(*hugepage_kobj);
 600         return err;
 601 }
 602
 603 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 604 {
 605         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
 606         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
 607         kobject_put(hugepage_kobj);
 608 }
 609 #else
 610 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
 611 {
 612         return 0;
 613 }
 614
 615 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
 616 {
 617 }
 618 #endif /* CONFIG_SYSFS */
 619
 620 static int __init hugepage_init(void)
 621 {
 622         int err;
 623         struct kobject *hugepage_kobj;
 624
 625         if (!has_transparent_hugepage()) {
 626                 transparent_hugepage_flags = 0;
 627                 return -EINVAL;
 628         }
 629
 630         err = hugepage_init_sysfs(&hugepage_kobj);
 631         if (err)
 632                 goto err_sysfs;
 633
 634         err = khugepaged_slab_init();
 635         if (err)
 636                 goto err_slab;
 637
 638         err = register_shrinker(&huge_zero_page_shrinker);
 639         if (err)
 640                 goto err_hzp_shrinker;
 641
 642         /*
 643          * By default disable transparent hugepages on smaller systems,
 644          * where the extra memory used could hurt more than TLB overhead
 645          * is likely to save.  The admin can still enable it through /sys.
 646          */
 647         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
 648                 transparent_hugepage_flags = 0;
 649                 return 0;
 650         }
 651
 652         err = start_stop_khugepaged();
 653         if (err)
 654                 goto err_khugepaged;
 655
 656         return 0;
 657 err_khugepaged:
 658         unregister_shrinker(&huge_zero_page_shrinker);
 659 err_hzp_shrinker:
 660         khugepaged_slab_exit();
 661 err_slab:
 662         hugepage_exit_sysfs(hugepage_kobj);
 663 err_sysfs:
 664         return err;
 665 }
 666 subsys_initcall(hugepage_init);
 667
 668 static int __init setup_transparent_hugepage(char *str)
 669 {
 670         int ret = 0;
 671         if (!str)
 672                 goto out;
 673         if (!strcmp(str, "always")) {
 674                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
 675                         &transparent_hugepage_flags);
 676                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 677                           &transparent_hugepage_flags);
 678                 ret = 1;
 679         } else if (!strcmp(str, "madvise")) {
 680                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 681                           &transparent_hugepage_flags);
 682                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 683                         &transparent_hugepage_flags);
 684                 ret = 1;
 685         } else if (!strcmp(str, "never")) {
 686                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
 687                           &transparent_hugepage_flags);
 688                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
 689                           &transparent_hugepage_flags);
 690                 ret = 1;
 691         }
 692 out:
 693         if (!ret)
 694                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
 695         return ret;
 696 }
 697 __setup("transparent_hugepage=", setup_transparent_hugepage);
 698
 699 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 700 {
 701         if (likely(vma->vm_flags & VM_WRITE))
 702                 pmd = pmd_mkwrite(pmd);
 703         return pmd;
 704 }
 705
 706 static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
 707 {
 708         pmd_t entry;
 709         entry = mk_pmd(page, prot);
 710         entry = pmd_mkhuge(entry);
 711         return entry;
 712 }
 713
 714 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
 715                                         struct vm_area_struct *vma,
 716                                         unsigned long address, pmd_t *pmd,
 717                                         struct page *page, gfp_t gfp,
 718                                         unsigned int flags)
 719 {
 720         struct mem_cgroup *memcg;
 721         pgtable_t pgtable;
 722         spinlock_t *ptl;
 723         unsigned long haddr = address & HPAGE_PMD_MASK;
 724
 725         VM_BUG_ON_PAGE(!PageCompound(page), page);
 726
 727         if (mem_cgroup_try_charge(page, mm, gfp, &memcg)) {
 728                 put_page(page);
 729                 count_vm_event(THP_FAULT_FALLBACK);
 730                 return VM_FAULT_FALLBACK;
 731         }
 732
 733         pgtable = pte_alloc_one(mm, haddr);
 734         if (unlikely(!pgtable)) {
 735                 mem_cgroup_cancel_charge(page, memcg);
 736                 put_page(page);
 737                 return VM_FAULT_OOM;
 738         }
 739
 740         clear_huge_page(page, haddr, HPAGE_PMD_NR);
 741         /*
 742          * The memory barrier inside __SetPageUptodate makes sure that
 743          * clear_huge_page writes become visible before the set_pmd_at()
 744          * write.
 745          */
 746         __SetPageUptodate(page);
 747
 748         ptl = pmd_lock(mm, pmd);
 749         if (unlikely(!pmd_none(*pmd))) {
 750                 spin_unlock(ptl);
 751                 mem_cgroup_cancel_charge(page, memcg);
 752                 put_page(page);
 753                 pte_free(mm, pgtable);
 754         } else {
 755                 pmd_t entry;
 756
 757                 /* Deliver the page fault to userland */
 758                 if (userfaultfd_missing(vma)) {
 759                         int ret;
 760
 761                         spin_unlock(ptl);
 762                         mem_cgroup_cancel_charge(page, memcg);
 763                         put_page(page);
 764                         pte_free(mm, pgtable);
 765                         ret = handle_userfault(vma, address, flags,
 766                                                VM_UFFD_MISSING);
 767                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 768                         return ret;
 769                 }
 770
 771                 entry = mk_huge_pmd(page, vma->vm_page_prot);
 772                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 773                 page_add_new_anon_rmap(page, vma, haddr);
 774                 mem_cgroup_commit_charge(page, memcg, false);
 775                 lru_cache_add_active_or_unevictable(page, vma);
 776                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
 777                 set_pmd_at(mm, haddr, pmd, entry);
 778                 add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
 779                 atomic_long_inc(&mm->nr_ptes);
 780                 spin_unlock(ptl);
 781                 count_vm_event(THP_FAULT_ALLOC);
 782         }
 783
 784         return 0;
 785 }
 786
 787 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
 788 {
 789         return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
 790 }
 791
 792 /* Caller must hold page table lock. */
 793 bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
 794                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
 795                 struct page *zero_page)
 796 {
 797         pmd_t entry;
 798         if (!pmd_none(*pmd))
 799                 return false;
 800         entry = mk_pmd(zero_page, vma->vm_page_prot);
 801         entry = pmd_mkhuge(entry);
 802         pgtable_trans_huge_deposit(mm, pmd, pgtable);
 803         set_pmd_at(mm, haddr, pmd, entry);
 804         atomic_long_inc(&mm->nr_ptes);
 805         return true;
 806 }
 807
 808 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 809                                unsigned long address, pmd_t *pmd,
 810                                unsigned int flags)
 811 {
 812         gfp_t gfp;
 813         struct page *page;
 814         unsigned long haddr = address & HPAGE_PMD_MASK;
 815
 816         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
 817                 return VM_FAULT_FALLBACK;
 818         if (unlikely(anon_vma_prepare(vma)))
 819                 return VM_FAULT_OOM;
 820         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
 821                 return VM_FAULT_OOM;
 822         if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
 823                         transparent_hugepage_use_zero_page()) {
 824                 spinlock_t *ptl;
 825                 pgtable_t pgtable;
 826                 struct page *zero_page;
 827                 bool set;
 828                 int ret;
 829                 pgtable = pte_alloc_one(mm, haddr);
 830                 if (unlikely(!pgtable))
 831                         return VM_FAULT_OOM;
 832                 zero_page = get_huge_zero_page();
 833                 if (unlikely(!zero_page)) {
 834                         pte_free(mm, pgtable);
 835                         count_vm_event(THP_FAULT_FALLBACK);
 836                         return VM_FAULT_FALLBACK;
 837                 }
 838                 ptl = pmd_lock(mm, pmd);
 839                 ret = 0;
 840                 set = false;
 841                 if (pmd_none(*pmd)) {
 842                         if (userfaultfd_missing(vma)) {
 843                                 spin_unlock(ptl);
 844                                 ret = handle_userfault(vma, address, flags,
 845                                                        VM_UFFD_MISSING);
 846                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
 847                         } else {
 848                                 set_huge_zero_page(pgtable, mm, vma,
 849                                                    haddr, pmd,
 850                                                    zero_page);
 851                                 spin_unlock(ptl);
 852                                 set = true;
 853                         }
 854                 } else
 855                         spin_unlock(ptl);
 856                 if (!set) {
 857                         pte_free(mm, pgtable);
 858                         put_huge_zero_page();
 859                 }
 860                 return ret;
 861         }
 862         gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
 863         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 864         if (unlikely(!page)) {
 865                 count_vm_event(THP_FAULT_FALLBACK);
 866                 return VM_FAULT_FALLBACK;
 867         }
 868         return __do_huge_pmd_anonymous_page(mm, vma, address, pmd, page, gfp,
 869                                             flags);
 870 }
 871
 872 static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 873                 pmd_t *pmd, unsigned long pfn, pgprot_t prot, bool write)
 874 {
 875         struct mm_struct *mm = vma->vm_mm;
 876         pmd_t entry;
 877         spinlock_t *ptl;
 878
 879         ptl = pmd_lock(mm, pmd);
 880         if (pmd_none(*pmd)) {
 881                 entry = pmd_mkhuge(pfn_pmd(pfn, prot));
 882                 if (write) {
 883                         entry = pmd_mkyoung(pmd_mkdirty(entry));
 884                         entry = maybe_pmd_mkwrite(entry, vma);
 885                 }
 886                 set_pmd_at(mm, addr, pmd, entry);
 887                 update_mmu_cache_pmd(vma, addr, pmd);
 888         }
 889         spin_unlock(ptl);
 890         return VM_FAULT_NOPAGE;
 891 }
 892
 893 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 894                         pmd_t *pmd, unsigned long pfn, bool write)
 895 {
 896         pgprot_t pgprot = vma->vm_page_prot;
 897         /*
 898          * If we had pmd_special, we could avoid all these restrictions,
 899          * but we need to be consistent with PTEs and architectures that
 900          * can't support a 'special' bit.
 901          */
 902         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
 903         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
 904                                                 (VM_PFNMAP|VM_MIXEDMAP));
 905         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
 906         BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
 907
 908         if (addr < vma->vm_start || addr >= vma->vm_end)
 909                 return VM_FAULT_SIGBUS;
 910         if (track_pfn_insert(vma, &pgprot, pfn))
 911                 return VM_FAULT_SIGBUS;
 912         return insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
 913 }
 914
 915 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 916                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
 917                   struct vm_area_struct *vma)
 918 {
 919         spinlock_t *dst_ptl, *src_ptl;
 920         struct page *src_page;
 921         pmd_t pmd;
 922         pgtable_t pgtable;
 923         int ret;
 924
 925         ret = -ENOMEM;
 926         pgtable = pte_alloc_one(dst_mm, addr);
 927         if (unlikely(!pgtable))
 928                 goto out;
 929
 930         dst_ptl = pmd_lock(dst_mm, dst_pmd);
 931         src_ptl = pmd_lockptr(src_mm, src_pmd);
 932         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
 933
 934         ret = -EAGAIN;
 935         pmd = *src_pmd;
 936         if (unlikely(!pmd_trans_huge(pmd))) {
 937                 pte_free(dst_mm, pgtable);
 938                 goto out_unlock;
 939         }
 940         /*
 941          * When page table lock is held, the huge zero pmd should not be
 942          * under splitting since we don't split the page itself, only pmd to
 943          * a page table.
 944          */
 945         if (is_huge_zero_pmd(pmd)) {
 946                 struct page *zero_page;
 947                 /*
 948                  * get_huge_zero_page() will never allocate a new page here,
 949                  * since we already have a zero page to copy. It just takes a
 950                  * reference.
 951                  */
 952                 zero_page = get_huge_zero_page();
 953                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
 954                                 zero_page);
 955                 ret = 0;
 956                 goto out_unlock;
 957         }
 958
 959         if (unlikely(pmd_trans_splitting(pmd))) {
 960                 /* split huge page running from under us */
 961                 spin_unlock(src_ptl);
 962                 spin_unlock(dst_ptl);
 963                 pte_free(dst_mm, pgtable);
 964
 965                 wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
 966                 goto out;
 967         }
 968         src_page = pmd_page(pmd);
 969         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
 970         get_page(src_page);
 971         page_dup_rmap(src_page);
 972         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
 973
 974         pmdp_set_wrprotect(src_mm, addr, src_pmd);
 975         pmd = pmd_mkold(pmd_wrprotect(pmd));
 976         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
 977         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
 978         atomic_long_inc(&dst_mm->nr_ptes);
 979
 980         ret = 0;
 981 out_unlock:
 982         spin_unlock(src_ptl);
 983         spin_unlock(dst_ptl);
 984 out:
 985         return ret;
 986 }
 987
 988 void huge_pmd_set_accessed(struct mm_struct *mm,
 989                            struct vm_area_struct *vma,
 990                            unsigned long address,
 991                            pmd_t *pmd, pmd_t orig_pmd,
 992                            int dirty)
 993 {
 994         spinlock_t *ptl;
 995         pmd_t entry;
 996         unsigned long haddr;
 997
 998         ptl = pmd_lock(mm, pmd);
 999         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1000                 goto unlock;
1001
1002         entry = pmd_mkyoung(orig_pmd);
1003         haddr = address & HPAGE_PMD_MASK;
1004         if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
1005                 update_mmu_cache_pmd(vma, address, pmd);
1006
1007 unlock:
1008         spin_unlock(ptl);
1009 }
1010
1011 /*
1012  * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
1013  * during copy_user_huge_page()'s copy_page_rep(): in the case when
1014  * the source page gets split and a tail freed before copy completes.
1015  * Called under pmd_lock of checked pmd, so safe from splitting itself.
1016  */
1017 static void get_user_huge_page(struct page *page)
1018 {
1019         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
1020                 struct page *endpage = page + HPAGE_PMD_NR;
1021
1022                 atomic_add(HPAGE_PMD_NR, &page->_count);
1023                 while (++page < endpage)
1024                         get_huge_page_tail(page);
1025         } else {
1026                 get_page(page);
1027         }
1028 }
1029
1030 static void put_user_huge_page(struct page *page)
1031 {
1032         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
1033                 struct page *endpage = page + HPAGE_PMD_NR;
1034
1035                 while (page < endpage)
1036                         put_page(page++);
1037         } else {
1038                 put_page(page);
1039         }
1040 }
1041
1042 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
1043                                         struct vm_area_struct *vma,
1044                                         unsigned long address,
1045                                         pmd_t *pmd, pmd_t orig_pmd,
1046                                         struct page *page,
1047                                         unsigned long haddr)
1048 {
1049         struct mem_cgroup *memcg;
1050         spinlock_t *ptl;
1051         pgtable_t pgtable;
1052         pmd_t _pmd;
1053         int ret = 0, i;
1054         struct page **pages;
1055         unsigned long mmun_start;       /* For mmu_notifiers */
1056         unsigned long mmun_end;         /* For mmu_notifiers */
1057
1058         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
1059                         GFP_KERNEL);
1060         if (unlikely(!pages)) {
1061                 ret |= VM_FAULT_OOM;
1062                 goto out;
1063         }
1064
1065         for (i = 0; i < HPAGE_PMD_NR; i++) {
1066                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
1067                                                __GFP_OTHER_NODE,
1068                                                vma, address, page_to_nid(page));
1069                 if (unlikely(!pages[i] ||
1070                              mem_cgroup_try_charge(pages[i], mm, GFP_KERNEL,
1071                                                    &memcg))) {
1072                         if (pages[i])
1073                                 put_page(pages[i]);
1074                         while (--i >= 0) {
1075                                 memcg = (void *)page_private(pages[i]);
1076                                 set_page_private(pages[i], 0);
1077                                 mem_cgroup_cancel_charge(pages[i], memcg);
1078                                 put_page(pages[i]);
1079                         }
1080                         kfree(pages);
1081                         ret |= VM_FAULT_OOM;
1082                         goto out;
1083                 }
1084                 set_page_private(pages[i], (unsigned long)memcg);
1085         }
1086
1087         for (i = 0; i < HPAGE_PMD_NR; i++) {
1088                 copy_user_highpage(pages[i], page + i,
1089                                    haddr + PAGE_SIZE * i, vma);
1090                 __SetPageUptodate(pages[i]);
1091                 cond_resched();
1092         }
1093
1094         mmun_start = haddr;
1095         mmun_end   = haddr + HPAGE_PMD_SIZE;
1096         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1097
1098         ptl = pmd_lock(mm, pmd);
1099         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1100                 goto out_free_pages;
1101         VM_BUG_ON_PAGE(!PageHead(page), page);
1102
1103         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1104         /* leave pmd empty until pte is filled */
1105
1106         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1107         pmd_populate(mm, &_pmd, pgtable);
1108
1109         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1110                 pte_t *pte, entry;
1111                 entry = mk_pte(pages[i], vma->vm_page_prot);
1112                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1113                 memcg = (void *)page_private(pages[i]);
1114                 set_page_private(pages[i], 0);
1115                 page_add_new_anon_rmap(pages[i], vma, haddr);
1116                 mem_cgroup_commit_charge(pages[i], memcg, false);
1117                 lru_cache_add_active_or_unevictable(pages[i], vma);
1118                 pte = pte_offset_map(&_pmd, haddr);
1119                 VM_BUG_ON(!pte_none(*pte));
1120                 set_pte_at(mm, haddr, pte, entry);
1121                 pte_unmap(pte);
1122         }
1123         kfree(pages);
1124
1125         smp_wmb(); /* make pte visible before pmd */
1126         pmd_populate(mm, pmd, pgtable);
1127         page_remove_rmap(page);
1128         spin_unlock(ptl);
1129
1130         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1131
1132         ret |= VM_FAULT_WRITE;
1133         put_page(page);
1134
1135 out:
1136         return ret;
1137
1138 out_free_pages:
1139         spin_unlock(ptl);
1140         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1141         for (i = 0; i < HPAGE_PMD_NR; i++) {
1142                 memcg = (void *)page_private(pages[i]);
1143                 set_page_private(pages[i], 0);
1144                 mem_cgroup_cancel_charge(pages[i], memcg);
1145                 put_page(pages[i]);
1146         }
1147         kfree(pages);
1148         goto out;
1149 }
1150
1151 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1152                         unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1153 {
1154         spinlock_t *ptl;
1155         int ret = 0;
1156         struct page *page = NULL, *new_page;
1157         struct mem_cgroup *memcg;
1158         unsigned long haddr;
1159         unsigned long mmun_start;       /* For mmu_notifiers */
1160         unsigned long mmun_end;         /* For mmu_notifiers */
1161         gfp_t huge_gfp;                 /* for allocation and charge */
1162
1163         ptl = pmd_lockptr(mm, pmd);
1164         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1165         haddr = address & HPAGE_PMD_MASK;
1166         if (is_huge_zero_pmd(orig_pmd))
1167                 goto alloc;
1168         spin_lock(ptl);
1169         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1170                 goto out_unlock;
1171
1172         page = pmd_page(orig_pmd);
1173         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1174         if (page_mapcount(page) == 1) {
1175                 pmd_t entry;
1176                 entry = pmd_mkyoung(orig_pmd);
1177                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1178                 if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1179                         update_mmu_cache_pmd(vma, address, pmd);
1180                 ret |= VM_FAULT_WRITE;
1181                 goto out_unlock;
1182         }
1183         get_user_huge_page(page);
1184         spin_unlock(ptl);
1185 alloc:
1186         if (transparent_hugepage_enabled(vma) &&
1187             !transparent_hugepage_debug_cow()) {
1188                 huge_gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
1189                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1190         } else
1191                 new_page = NULL;
1192
1193         if (unlikely(!new_page)) {
1194                 if (!page) {
1195                         split_huge_page_pmd(vma, address, pmd);
1196                         ret |= VM_FAULT_FALLBACK;
1197                 } else {
1198                         ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1199                                         pmd, orig_pmd, page, haddr);
1200                         if (ret & VM_FAULT_OOM) {
1201                                 split_huge_page(page);
1202                                 ret |= VM_FAULT_FALLBACK;
1203                         }
1204                         put_user_huge_page(page);
1205                 }
1206                 count_vm_event(THP_FAULT_FALLBACK);
1207                 goto out;
1208         }
1209
1210         if (unlikely(mem_cgroup_try_charge(new_page, mm, huge_gfp, &memcg))) {
1211                 put_page(new_page);
1212                 if (page) {
1213                         split_huge_page(page);
1214                         put_user_huge_page(page);
1215                 } else
1216                         split_huge_page_pmd(vma, address, pmd);
1217                 ret |= VM_FAULT_FALLBACK;
1218                 count_vm_event(THP_FAULT_FALLBACK);
1219                 goto out;
1220         }
1221
1222         count_vm_event(THP_FAULT_ALLOC);
1223
1224         if (!page)
1225                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1226         else
1227                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1228         __SetPageUptodate(new_page);
1229
1230         mmun_start = haddr;
1231         mmun_end   = haddr + HPAGE_PMD_SIZE;
1232         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1233
1234         spin_lock(ptl);
1235         if (page)
1236                 put_user_huge_page(page);
1237         if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1238                 spin_unlock(ptl);
1239                 mem_cgroup_cancel_charge(new_page, memcg);
1240                 put_page(new_page);
1241                 goto out_mn;
1242         } else {
1243                 pmd_t entry;
1244                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1245                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1246                 pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1247                 page_add_new_anon_rmap(new_page, vma, haddr);
1248                 mem_cgroup_commit_charge(new_page, memcg, false);
1249                 lru_cache_add_active_or_unevictable(new_page, vma);
1250                 set_pmd_at(mm, haddr, pmd, entry);
1251                 update_mmu_cache_pmd(vma, address, pmd);
1252                 if (!page) {
1253                         add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1254                         put_huge_zero_page();
1255                 } else {
1256                         VM_BUG_ON_PAGE(!PageHead(page), page);
1257                         page_remove_rmap(page);
1258                         put_page(page);
1259                 }
1260                 ret |= VM_FAULT_WRITE;
1261         }
1262         spin_unlock(ptl);
1263 out_mn:
1264         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1265 out:
1266         return ret;
1267 out_unlock:
1268         spin_unlock(ptl);
1269         return ret;
1270 }
1271
1272 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1273                                    unsigned long addr,
1274                                    pmd_t *pmd,
1275                                    unsigned int flags)
1276 {
1277         struct mm_struct *mm = vma->vm_mm;
1278         struct page *page = NULL;
1279
1280         assert_spin_locked(pmd_lockptr(mm, pmd));
1281
1282         if (flags & FOLL_WRITE && !pmd_write(*pmd))
1283                 goto out;
1284
1285         /* Avoid dumping huge zero page */
1286         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1287                 return ERR_PTR(-EFAULT);
1288
1289         /* Full NUMA hinting faults to serialise migration in fault paths */
1290         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1291                 goto out;
1292
1293         page = pmd_page(*pmd);
1294         VM_BUG_ON_PAGE(!PageHead(page), page);
1295         if (flags & FOLL_TOUCH) {
1296                 pmd_t _pmd;
1297                 /*
1298                  * We should set the dirty bit only for FOLL_WRITE but
1299                  * for now the dirty bit in the pmd is meaningless.
1300                  * And if the dirty bit will become meaningful and
1301                  * we'll only set it with FOLL_WRITE, an atomic
1302                  * set_bit will be required on the pmd to set the
1303                  * young bit, instead of the current set_pmd_at.
1304                  */
1305                 _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1306                 if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1307                                           pmd, _pmd,  1))
1308                         update_mmu_cache_pmd(vma, addr, pmd);
1309         }
1310         if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
1311                 if (page->mapping && trylock_page(page)) {
1312                         lru_add_drain();
1313                         if (page->mapping)
1314                                 mlock_vma_page(page);
1315                         unlock_page(page);
1316                 }
1317         }
1318         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1319         VM_BUG_ON_PAGE(!PageCompound(page), page);
1320         if (flags & FOLL_GET)
1321                 get_page_foll(page);
1322
1323 out:
1324         return page;
1325 }
1326
1327 /* NUMA hinting page fault entry point for trans huge pmds */
1328 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1329                                 unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1330 {
1331         spinlock_t *ptl;
1332         struct anon_vma *anon_vma = NULL;
1333         struct page *page;
1334         unsigned long haddr = addr & HPAGE_PMD_MASK;
1335         int page_nid = -1, this_nid = numa_node_id();
1336         int target_nid, last_cpupid = -1;
1337         bool page_locked;
1338         bool migrated = false;
1339         bool was_writable;
1340         int flags = 0;
1341
1342         /* A PROT_NONE fault should not end up here */
1343         BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
1344
1345         ptl = pmd_lock(mm, pmdp);
1346         if (unlikely(!pmd_same(pmd, *pmdp)))
1347                 goto out_unlock;
1348
1349         /*
1350          * If there are potential migrations, wait for completion and retry
1351          * without disrupting NUMA hinting information. Do not relock and
1352          * check_same as the page may no longer be mapped.
1353          */
1354         if (unlikely(pmd_trans_migrating(*pmdp))) {
1355                 page = pmd_page(*pmdp);
1356                 spin_unlock(ptl);
1357                 wait_on_page_locked(page);
1358                 goto out;
1359         }
1360
1361         page = pmd_page(pmd);
1362         BUG_ON(is_huge_zero_page(page));
1363         page_nid = page_to_nid(page);
1364         last_cpupid = page_cpupid_last(page);
1365         count_vm_numa_event(NUMA_HINT_FAULTS);
1366         if (page_nid == this_nid) {
1367                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1368                 flags |= TNF_FAULT_LOCAL;
1369         }
1370
1371         /* See similar comment in do_numa_page for explanation */
1372         if (!(vma->vm_flags & VM_WRITE))
1373                 flags |= TNF_NO_GROUP;
1374
1375         /*
1376          * Acquire the page lock to serialise THP migrations but avoid dropping
1377          * page_table_lock if at all possible
1378          */
1379         page_locked = trylock_page(page);
1380         target_nid = mpol_misplaced(page, vma, haddr);
1381         if (target_nid == -1) {
1382                 /* If the page was locked, there are no parallel migrations */
1383                 if (page_locked)
1384                         goto clear_pmdnuma;
1385         }
1386
1387         /* Migration could have started since the pmd_trans_migrating check */
1388         if (!page_locked) {
1389                 spin_unlock(ptl);
1390                 wait_on_page_locked(page);
1391                 page_nid = -1;
1392                 goto out;
1393         }
1394
1395         /*
1396          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1397          * to serialises splits
1398          */
1399         get_page(page);
1400         spin_unlock(ptl);
1401         anon_vma = page_lock_anon_vma_read(page);
1402
1403         /* Confirm the PMD did not change while page_table_lock was released */
1404         spin_lock(ptl);
1405         if (unlikely(!pmd_same(pmd, *pmdp))) {
1406                 unlock_page(page);
1407                 put_page(page);
1408                 page_nid = -1;
1409                 goto out_unlock;
1410         }
1411
1412         /* Bail if we fail to protect against THP splits for any reason */
1413         if (unlikely(!anon_vma)) {
1414                 put_page(page);
1415                 page_nid = -1;
1416                 goto clear_pmdnuma;
1417         }
1418
1419         /*
1420          * Migrate the THP to the requested node, returns with page unlocked
1421          * and access rights restored.
1422          */
1423         spin_unlock(ptl);
1424         migrated = migrate_misplaced_transhuge_page(mm, vma,
1425                                 pmdp, pmd, addr, page, target_nid);
1426         if (migrated) {
1427                 flags |= TNF_MIGRATED;
1428                 page_nid = target_nid;
1429         } else
1430                 flags |= TNF_MIGRATE_FAIL;
1431
1432         goto out;
1433 clear_pmdnuma:
1434         BUG_ON(!PageLocked(page));
1435         was_writable = pmd_write(pmd);
1436         pmd = pmd_modify(pmd, vma->vm_page_prot);
1437         pmd = pmd_mkyoung(pmd);
1438         if (was_writable)
1439                 pmd = pmd_mkwrite(pmd);
1440         set_pmd_at(mm, haddr, pmdp, pmd);
1441         update_mmu_cache_pmd(vma, addr, pmdp);
1442         unlock_page(page);
1443 out_unlock:
1444         spin_unlock(ptl);
1445
1446 out:
1447         if (anon_vma)
1448                 page_unlock_anon_vma_read(anon_vma);
1449
1450         if (page_nid != -1)
1451                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
1452
1453         return 0;
1454 }
1455
1456 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1457                  pmd_t *pmd, unsigned long addr)
1458 {
1459         spinlock_t *ptl;
1460         int ret = 0;
1461
1462         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1463                 pgtable_t pgtable;
1464                 pmd_t orig_pmd;
1465                 /*
1466                  * For architectures like ppc64 we look at deposited pgtable
1467                  * when calling pmdp_huge_get_and_clear. So do the
1468                  * pgtable_trans_huge_withdraw after finishing pmdp related
1469                  * operations.
1470                  */
1471                 orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1472                                                         tlb->fullmm);
1473                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1474                 if (vma_is_dax(vma)) {
1475                         if (is_huge_zero_pmd(orig_pmd)) {
1476                                 pgtable = NULL;
1477                         } else {
1478                                 spin_unlock(ptl);
1479                                 return 1;
1480                         }
1481                 } else {
1482                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1483                 }
1484                 if (is_huge_zero_pmd(orig_pmd)) {
1485                         atomic_long_dec(&tlb->mm->nr_ptes);
1486                         spin_unlock(ptl);
1487                         put_huge_zero_page();
1488                 } else {
1489                         struct page *page = pmd_page(orig_pmd);
1490                         page_remove_rmap(page);
1491                         VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1492                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1493                         VM_BUG_ON_PAGE(!PageHead(page), page);
1494                         atomic_long_dec(&tlb->mm->nr_ptes);
1495                         spin_unlock(ptl);
1496                         tlb_remove_page(tlb, page);
1497                 }
1498                 if (pgtable)
1499                         pte_free(tlb->mm, pgtable);
1500                 ret = 1;
1501         }
1502         return ret;
1503 }
1504
1505 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1506                   unsigned long old_addr,
1507                   unsigned long new_addr, unsigned long old_end,
1508                   pmd_t *old_pmd, pmd_t *new_pmd)
1509 {
1510         spinlock_t *old_ptl, *new_ptl;
1511         int ret = 0;
1512         pmd_t pmd;
1513
1514         struct mm_struct *mm = vma->vm_mm;
1515
1516         if ((old_addr & ~HPAGE_PMD_MASK) ||
1517             (new_addr & ~HPAGE_PMD_MASK) ||
1518             old_end - old_addr < HPAGE_PMD_SIZE ||
1519             (new_vma->vm_flags & VM_NOHUGEPAGE))
1520                 goto out;
1521
1522         /*
1523          * The destination pmd shouldn't be established, free_pgtables()
1524          * should have release it.
1525          */
1526         if (WARN_ON(!pmd_none(*new_pmd))) {
1527                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1528                 goto out;
1529         }
1530
1531         /*
1532          * We don't have to worry about the ordering of src and dst
1533          * ptlocks because exclusive mmap_sem prevents deadlock.
1534          */
1535         ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
1536         if (ret == 1) {
1537                 new_ptl = pmd_lockptr(mm, new_pmd);
1538                 if (new_ptl != old_ptl)
1539                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1540                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1541                 VM_BUG_ON(!pmd_none(*new_pmd));
1542
1543                 if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
1544                         pgtable_t pgtable;
1545                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1546                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1547                 }
1548                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1549                 if (new_ptl != old_ptl)
1550                         spin_unlock(new_ptl);
1551                 spin_unlock(old_ptl);
1552         }
1553 out:
1554         return ret;
1555 }
1556
1557 /*
1558  * Returns
1559  *  - 0 if PMD could not be locked
1560  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1561  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1562  */
1563 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1564                 unsigned long addr, pgprot_t newprot, int prot_numa)
1565 {
1566         struct mm_struct *mm = vma->vm_mm;
1567         spinlock_t *ptl;
1568         int ret = 0;
1569
1570         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1571                 pmd_t entry;
1572                 bool preserve_write = prot_numa && pmd_write(*pmd);
1573                 ret = 1;
1574
1575                 /*
1576                  * Avoid trapping faults against the zero page. The read-only
1577                  * data is likely to be read-cached on the local CPU and
1578                  * local/remote hits to the zero page are not interesting.
1579                  */
1580                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
1581                         spin_unlock(ptl);
1582                         return ret;
1583                 }
1584
1585                 if (!prot_numa || !pmd_protnone(*pmd)) {
1586                         entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
1587                         entry = pmd_modify(entry, newprot);
1588                         if (preserve_write)
1589                                 entry = pmd_mkwrite(entry);
1590                         ret = HPAGE_PMD_NR;
1591                         set_pmd_at(mm, addr, pmd, entry);
1592                         BUG_ON(!preserve_write && pmd_write(entry));
1593                 }
1594                 spin_unlock(ptl);
1595         }
1596
1597         return ret;
1598 }
1599
1600 /*
1601  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1602  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1603  *
1604  * Note that if it returns 1, this routine returns without unlocking page
1605  * table locks. So callers must unlock them.
1606  */
1607 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
1608                 spinlock_t **ptl)
1609 {
1610         *ptl = pmd_lock(vma->vm_mm, pmd);
1611         if (likely(pmd_trans_huge(*pmd))) {
1612                 if (unlikely(pmd_trans_splitting(*pmd))) {
1613                         spin_unlock(*ptl);
1614                         wait_split_huge_page(vma->anon_vma, pmd);
1615                         return -1;
1616                 } else {
1617                         /* Thp mapped by 'pmd' is stable, so we can
1618                          * handle it as it is. */
1619                         return 1;
1620                 }
1621         }
1622         spin_unlock(*ptl);
1623         return 0;
1624 }
1625
1626 /*
1627  * This function returns whether a given @page is mapped onto the @address
1628  * in the virtual space of @mm.
1629  *
1630  * When it's true, this function returns *pmd with holding the page table lock
1631  * and passing it back to the caller via @ptl.
1632  * If it's false, returns NULL without holding the page table lock.
1633  */
1634 pmd_t *page_check_address_pmd(struct page *page,
1635                               struct mm_struct *mm,
1636                               unsigned long address,
1637                               enum page_check_address_pmd_flag flag,
1638                               spinlock_t **ptl)
1639 {
1640         pgd_t *pgd;
1641         pud_t *pud;
1642         pmd_t *pmd;
1643
1644         if (address & ~HPAGE_PMD_MASK)
1645                 return NULL;
1646
1647         pgd = pgd_offset(mm, address);
1648         if (!pgd_present(*pgd))
1649                 return NULL;
1650         pud = pud_offset(pgd, address);
1651         if (!pud_present(*pud))
1652                 return NULL;
1653         pmd = pmd_offset(pud, address);
1654
1655         *ptl = pmd_lock(mm, pmd);
1656         if (!pmd_present(*pmd))
1657                 goto unlock;
1658         if (pmd_page(*pmd) != page)
1659                 goto unlock;
1660         /*
1661          * split_vma() may create temporary aliased mappings. There is
1662          * no risk as long as all huge pmd are found and have their
1663          * splitting bit set before __split_huge_page_refcount
1664          * runs. Finding the same huge pmd more than once during the
1665          * same rmap walk is not a problem.
1666          */
1667         if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1668             pmd_trans_splitting(*pmd))
1669                 goto unlock;
1670         if (pmd_trans_huge(*pmd)) {
1671                 VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1672                           !pmd_trans_splitting(*pmd));
1673                 return pmd;
1674         }
1675 unlock:
1676         spin_unlock(*ptl);
1677         return NULL;
1678 }
1679
1680 static int __split_huge_page_splitting(struct page *page,
1681                                        struct vm_area_struct *vma,
1682                                        unsigned long address)
1683 {
1684         struct mm_struct *mm = vma->vm_mm;
1685         spinlock_t *ptl;
1686         pmd_t *pmd;
1687         int ret = 0;
1688         /* For mmu_notifiers */
1689         const unsigned long mmun_start = address;
1690         const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1691
1692         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1693         pmd = page_check_address_pmd(page, mm, address,
1694                         PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
1695         if (pmd) {
1696                 /*
1697                  * We can't temporarily set the pmd to null in order
1698                  * to split it, the pmd must remain marked huge at all
1699                  * times or the VM won't take the pmd_trans_huge paths
1700                  * and it won't wait on the anon_vma->root->rwsem to
1701                  * serialize against split_huge_page*.
1702                  */
1703                 pmdp_splitting_flush(vma, address, pmd);
1704
1705                 ret = 1;
1706                 spin_unlock(ptl);
1707         }
1708         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1709
1710         return ret;
1711 }
1712
1713 static void __split_huge_page_refcount(struct page *page,
1714                                        struct list_head *list)
1715 {
1716         int i;
1717         struct zone *zone = page_zone(page);
1718         struct lruvec *lruvec;
1719         int tail_count = 0;
1720
1721         /* prevent PageLRU to go away from under us, and freeze lru stats */
1722         spin_lock_irq(&zone->lru_lock);
1723         lruvec = mem_cgroup_page_lruvec(page, zone);
1724
1725         compound_lock(page);
1726         /* complete memcg works before add pages to LRU */
1727         mem_cgroup_split_huge_fixup(page);
1728
1729         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1730                 struct page *page_tail = page + i;
1731
1732                 /* tail_page->_mapcount cannot change */
1733                 BUG_ON(page_mapcount(page_tail) < 0);
1734                 tail_count += page_mapcount(page_tail);
1735                 /* check for overflow */
1736                 BUG_ON(tail_count < 0);
1737                 BUG_ON(atomic_read(&page_tail->_count) != 0);
1738                 /*
1739                  * tail_page->_count is zero and not changing from
1740                  * under us. But get_page_unless_zero() may be running
1741                  * from under us on the tail_page. If we used
1742                  * atomic_set() below instead of atomic_add(), we
1743                  * would then run atomic_set() concurrently with
1744                  * get_page_unless_zero(), and atomic_set() is
1745                  * implemented in C not using locked ops. spin_unlock
1746                  * on x86 sometime uses locked ops because of PPro
1747                  * errata 66, 92, so unless somebody can guarantee
1748                  * atomic_set() here would be safe on all archs (and
1749                  * not only on x86), it's safer to use atomic_add().
1750                  */
1751                 atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1752                            &page_tail->_count);
1753
1754                 /* after clearing PageTail the gup refcount can be released */
1755                 smp_mb__after_atomic();
1756
1757                 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1758                 page_tail->flags |= (page->flags &
1759                                      ((1L << PG_referenced) |
1760                                       (1L << PG_swapbacked) |
1761                                       (1L << PG_mlocked) |
1762                                       (1L << PG_uptodate) |
1763                                       (1L << PG_active) |
1764                                       (1L << PG_unevictable)));
1765                 page_tail->flags |= (1L << PG_dirty);
1766
1767                 /* clear PageTail before overwriting first_page */
1768                 smp_wmb();
1769
1770                 /*
1771                  * __split_huge_page_splitting() already set the
1772                  * splitting bit in all pmd that could map this
1773                  * hugepage, that will ensure no CPU can alter the
1774                  * mapcount on the head page. The mapcount is only
1775                  * accounted in the head page and it has to be
1776                  * transferred to all tail pages in the below code. So
1777                  * for this code to be safe, the split the mapcount
1778                  * can't change. But that doesn't mean userland can't
1779                  * keep changing and reading the page contents while
1780                  * we transfer the mapcount, so the pmd splitting
1781                  * status is achieved setting a reserved bit in the
1782                  * pmd, not by clearing the present bit.
1783                 */
1784                 page_tail->_mapcount = page->_mapcount;
1785
1786                 BUG_ON(page_tail->mapping);
1787                 page_tail->mapping = page->mapping;
1788
1789                 page_tail->index = page->index + i;
1790                 page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
1791
1792                 BUG_ON(!PageAnon(page_tail));
1793                 BUG_ON(!PageUptodate(page_tail));
1794                 BUG_ON(!PageDirty(page_tail));
1795                 BUG_ON(!PageSwapBacked(page_tail));
1796
1797                 lru_add_page_tail(page, page_tail, lruvec, list);
1798         }
1799         atomic_sub(tail_count, &page->_count);
1800         BUG_ON(atomic_read(&page->_count) <= 0);
1801
1802         __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1803
1804         ClearPageCompound(page);
1805         compound_unlock(page);
1806         spin_unlock_irq(&zone->lru_lock);
1807
1808         for (i = 1; i < HPAGE_PMD_NR; i++) {
1809                 struct page *page_tail = page + i;
1810                 BUG_ON(page_count(page_tail) <= 0);
1811                 /*
1812                  * Tail pages may be freed if there wasn't any mapping
1813                  * like if add_to_swap() is running on a lru page that
1814                  * had its mapping zapped. And freeing these pages
1815                  * requires taking the lru_lock so we do the put_page
1816                  * of the tail pages after the split is complete.
1817                  */
1818                 put_page(page_tail);
1819         }
1820
1821         /*
1822          * Only the head page (now become a regular page) is required
1823          * to be pinned by the caller.
1824          */
1825         BUG_ON(page_count(page) <= 0);
1826 }
1827
1828 static int __split_huge_page_map(struct page *page,
1829                                  struct vm_area_struct *vma,
1830                                  unsigned long address)
1831 {
1832         struct mm_struct *mm = vma->vm_mm;
1833         spinlock_t *ptl;
1834         pmd_t *pmd, _pmd;
1835         int ret = 0, i;
1836         pgtable_t pgtable;
1837         unsigned long haddr;
1838
1839         pmd = page_check_address_pmd(page, mm, address,
1840                         PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
1841         if (pmd) {
1842                 pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1843                 pmd_populate(mm, &_pmd, pgtable);
1844                 if (pmd_write(*pmd))
1845                         BUG_ON(page_mapcount(page) != 1);
1846
1847                 haddr = address;
1848                 for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1849                         pte_t *pte, entry;
1850                         BUG_ON(PageCompound(page+i));
1851                         /*
1852                          * Note that NUMA hinting access restrictions are not
1853                          * transferred to avoid any possibility of altering
1854                          * permissions across VMAs.
1855                          */
1856                         entry = mk_pte(page + i, vma->vm_page_prot);
1857                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1858                         if (!pmd_write(*pmd))
1859                                 entry = pte_wrprotect(entry);
1860                         if (!pmd_young(*pmd))
1861                                 entry = pte_mkold(entry);
1862                         pte = pte_offset_map(&_pmd, haddr);
1863                         BUG_ON(!pte_none(*pte));
1864                         set_pte_at(mm, haddr, pte, entry);
1865                         pte_unmap(pte);
1866                 }
1867
1868                 smp_wmb(); /* make pte visible before pmd */
1869                 /*
1870                  * Up to this point the pmd is present and huge and
1871                  * userland has the whole access to the hugepage
1872                  * during the split (which happens in place). If we
1873                  * overwrite the pmd with the not-huge version
1874                  * pointing to the pte here (which of course we could
1875                  * if all CPUs were bug free), userland could trigger
1876                  * a small page size TLB miss on the small sized TLB
1877                  * while the hugepage TLB entry is still established
1878                  * in the huge TLB. Some CPU doesn't like that. See
1879                  * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1880                  * Erratum 383 on page 93. Intel should be safe but is
1881                  * also warns that it's only safe if the permission
1882                  * and cache attributes of the two entries loaded in
1883                  * the two TLB is identical (which should be the case
1884                  * here). But it is generally safer to never allow
1885                  * small and huge TLB entries for the same virtual
1886                  * address to be loaded simultaneously. So instead of
1887                  * doing "pmd_populate(); flush_tlb_range();" we first
1888                  * mark the current pmd notpresent (atomically because
1889                  * here the pmd_trans_huge and pmd_trans_splitting
1890                  * must remain set at all times on the pmd until the
1891                  * split is complete for this pmd), then we flush the
1892                  * SMP TLB and finally we write the non-huge version
1893                  * of the pmd entry with pmd_populate.
1894                  */
1895                 pmdp_invalidate(vma, address, pmd);
1896                 pmd_populate(mm, pmd, pgtable);
1897                 ret = 1;
1898                 spin_unlock(ptl);
1899         }
1900
1901         return ret;
1902 }
1903
1904 /* must be called with anon_vma->root->rwsem held */
1905 static void __split_huge_page(struct page *page,
1906                               struct anon_vma *anon_vma,
1907                               struct list_head *list)
1908 {
1909         int mapcount, mapcount2;
1910         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1911         struct anon_vma_chain *avc;
1912
1913         BUG_ON(!PageHead(page));
1914         BUG_ON(PageTail(page));
1915
1916         mapcount = 0;
1917         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1918                 struct vm_area_struct *vma = avc->vma;
1919                 unsigned long addr = vma_address(page, vma);
1920                 BUG_ON(is_vma_temporary_stack(vma));
1921                 mapcount += __split_huge_page_splitting(page, vma, addr);
1922         }
1923         /*
1924          * It is critical that new vmas are added to the tail of the
1925          * anon_vma list. This guarantes that if copy_huge_pmd() runs
1926          * and establishes a child pmd before
1927          * __split_huge_page_splitting() freezes the parent pmd (so if
1928          * we fail to prevent copy_huge_pmd() from running until the
1929          * whole __split_huge_page() is complete), we will still see
1930          * the newly established pmd of the child later during the
1931          * walk, to be able to set it as pmd_trans_splitting too.
1932          */
1933         if (mapcount != page_mapcount(page)) {
1934                 pr_err("mapcount %d page_mapcount %d\n",
1935                         mapcount, page_mapcount(page));
1936                 BUG();
1937         }
1938
1939         __split_huge_page_refcount(page, list);
1940
1941         mapcount2 = 0;
1942         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1943                 struct vm_area_struct *vma = avc->vma;
1944                 unsigned long addr = vma_address(page, vma);
1945                 BUG_ON(is_vma_temporary_stack(vma));
1946                 mapcount2 += __split_huge_page_map(page, vma, addr);
1947         }
1948         if (mapcount != mapcount2) {
1949                 pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
1950                         mapcount, mapcount2, page_mapcount(page));
1951                 BUG();
1952         }
1953 }
1954
1955 /*
1956  * Split a hugepage into normal pages. This doesn't change the position of head
1957  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1958  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1959  * from the hugepage.
1960  * Return 0 if the hugepage is split successfully otherwise return 1.
1961  */
1962 int split_huge_page_to_list(struct page *page, struct list_head *list)
1963 {
1964         struct anon_vma *anon_vma;
1965         int ret = 1;
1966
1967         BUG_ON(is_huge_zero_page(page));
1968         BUG_ON(!PageAnon(page));
1969
1970         /*
1971          * The caller does not necessarily hold an mmap_sem that would prevent
1972          * the anon_vma disappearing so we first we take a reference to it
1973          * and then lock the anon_vma for write. This is similar to
1974          * page_lock_anon_vma_read except the write lock is taken to serialise
1975          * against parallel split or collapse operations.
1976          */
1977         anon_vma = page_get_anon_vma(page);
1978         if (!anon_vma)
1979                 goto out;
1980         anon_vma_lock_write(anon_vma);
1981
1982         ret = 0;
1983         if (!PageCompound(page))
1984                 goto out_unlock;
1985
1986         BUG_ON(!PageSwapBacked(page));
1987         __split_huge_page(page, anon_vma, list);
1988         count_vm_event(THP_SPLIT);
1989
1990         BUG_ON(PageCompound(page));
1991 out_unlock:
1992         anon_vma_unlock_write(anon_vma);
1993         put_anon_vma(anon_vma);
1994 out:
1995         return ret;
1996 }
1997
1998 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
1999
2000 int hugepage_madvise(struct vm_area_struct *vma,
2001                      unsigned long *vm_flags, int advice)
2002 {
2003         switch (advice) {
2004         case MADV_HUGEPAGE:
2005 #ifdef CONFIG_S390
2006                 /*
2007                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
2008                  * can't handle this properly after s390_enable_sie, so we simply
2009                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
2010                  */
2011                 if (mm_has_pgste(vma->vm_mm))
2012                         return 0;
2013 #endif
2014                 /*
2015                  * Be somewhat over-protective like KSM for now!
2016                  */
2017                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
2018                         return -EINVAL;
2019                 *vm_flags &= ~VM_NOHUGEPAGE;
2020                 *vm_flags |= VM_HUGEPAGE;
2021                 /*
2022                  * If the vma become good for khugepaged to scan,
2023                  * register it here without waiting a page fault that
2024                  * may not happen any time soon.
2025                  */
2026                 if (unlikely(khugepaged_enter_vma_merge(vma, *vm_flags)))
2027                         return -ENOMEM;
2028                 break;
2029         case MADV_NOHUGEPAGE:
2030                 /*
2031                  * Be somewhat over-protective like KSM for now!
2032                  */
2033                 if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
2034                         return -EINVAL;
2035                 *vm_flags &= ~VM_HUGEPAGE;
2036                 *vm_flags |= VM_NOHUGEPAGE;
2037                 /*
2038                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
2039                  * this vma even if we leave the mm registered in khugepaged if
2040                  * it got registered before VM_NOHUGEPAGE was set.
2041                  */
2042                 break;
2043         }
2044
2045         return 0;
2046 }
2047
2048 static int __init khugepaged_slab_init(void)
2049 {
2050         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
2051                                           sizeof(struct mm_slot),
2052                                           __alignof__(struct mm_slot), 0, NULL);
2053         if (!mm_slot_cache)
2054                 return -ENOMEM;
2055
2056         return 0;
2057 }
2058
2059 static void __init khugepaged_slab_exit(void)
2060 {
2061         kmem_cache_destroy(mm_slot_cache);
2062 }
2063
2064 static inline struct mm_slot *alloc_mm_slot(void)
2065 {
2066         if (!mm_slot_cache)     /* initialization failed */
2067                 return NULL;
2068         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
2069 }
2070
2071 static inline void free_mm_slot(struct mm_slot *mm_slot)
2072 {
2073         kmem_cache_free(mm_slot_cache, mm_slot);
2074 }
2075
2076 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
2077 {
2078         struct mm_slot *mm_slot;
2079
2080         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
2081                 if (mm == mm_slot->mm)
2082                         return mm_slot;
2083
2084         return NULL;
2085 }
2086
2087 static void insert_to_mm_slots_hash(struct mm_struct *mm,
2088                                     struct mm_slot *mm_slot)
2089 {
2090         mm_slot->mm = mm;
2091         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
2092 }
2093
2094 static inline int khugepaged_test_exit(struct mm_struct *mm)
2095 {
2096         return atomic_read(&mm->mm_users) == 0;
2097 }
2098
2099 int __khugepaged_enter(struct mm_struct *mm)
2100 {
2101         struct mm_slot *mm_slot;
2102         int wakeup;
2103
2104         mm_slot = alloc_mm_slot();
2105         if (!mm_slot)
2106                 return -ENOMEM;
2107
2108         /* __khugepaged_exit() must not run from under us */
2109         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
2110         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
2111                 free_mm_slot(mm_slot);
2112                 return 0;
2113         }
2114
2115         spin_lock(&khugepaged_mm_lock);
2116         insert_to_mm_slots_hash(mm, mm_slot);
2117         /*
2118          * Insert just behind the scanning cursor, to let the area settle
2119          * down a little.
2120          */
2121         wakeup = list_empty(&khugepaged_scan.mm_head);
2122         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
2123         spin_unlock(&khugepaged_mm_lock);
2124
2125         atomic_inc(&mm->mm_count);
2126         if (wakeup)
2127                 wake_up_interruptible(&khugepaged_wait);
2128
2129         return 0;
2130 }
2131
2132 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
2133                                unsigned long vm_flags)
2134 {
2135         unsigned long hstart, hend;
2136         if (!vma->anon_vma)
2137                 /*
2138                  * Not yet faulted in so we will register later in the
2139                  * page fault if needed.
2140                  */
2141                 return 0;
2142         if (vma->vm_ops)
2143                 /* khugepaged not yet working on file or special mappings */
2144                 return 0;
2145         VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
2146         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2147         hend = vma->vm_end & HPAGE_PMD_MASK;
2148         if (hstart < hend)
2149                 return khugepaged_enter(vma, vm_flags);
2150         return 0;
2151 }
2152
2153 void __khugepaged_exit(struct mm_struct *mm)
2154 {
2155         struct mm_slot *mm_slot;
2156         int free = 0;
2157
2158         spin_lock(&khugepaged_mm_lock);
2159         mm_slot = get_mm_slot(mm);
2160         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2161                 hash_del(&mm_slot->hash);
2162                 list_del(&mm_slot->mm_node);
2163                 free = 1;
2164         }
2165         spin_unlock(&khugepaged_mm_lock);
2166
2167         if (free) {
2168                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2169                 free_mm_slot(mm_slot);
2170                 mmdrop(mm);
2171         } else if (mm_slot) {
2172                 /*
2173                  * This is required to serialize against
2174                  * khugepaged_test_exit() (which is guaranteed to run
2175                  * under mmap sem read mode). Stop here (after we
2176                  * return all pagetables will be destroyed) until
2177                  * khugepaged has finished working on the pagetables
2178                  * under the mmap_sem.
2179                  */
2180                 down_write(&mm->mmap_sem);
2181                 up_write(&mm->mmap_sem);
2182         }
2183 }
2184
2185 static void release_pte_page(struct page *page)
2186 {
2187         /* 0 stands for page_is_file_cache(page) == false */
2188         dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2189         unlock_page(page);
2190         putback_lru_page(page);
2191 }
2192
2193 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2194 {
2195         while (--_pte >= pte) {
2196                 pte_t pteval = *_pte;
2197                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
2198                         release_pte_page(pte_page(pteval));
2199         }
2200 }
2201
2202 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2203                                         unsigned long address,
2204                                         pte_t *pte)
2205 {
2206         struct page *page;
2207         pte_t *_pte;
2208         int none_or_zero = 0;
2209         bool referenced = false, writable = false;
2210         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2211              _pte++, address += PAGE_SIZE) {
2212                 pte_t pteval = *_pte;
2213                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2214                         if (!userfaultfd_armed(vma) &&
2215                             ++none_or_zero <= khugepaged_max_ptes_none)
2216                                 continue;
2217                         else
2218                                 goto out;
2219                 }
2220                 if (!pte_present(pteval))
2221                         goto out;
2222                 page = vm_normal_page(vma, address, pteval);
2223                 if (unlikely(!page))
2224                         goto out;
2225
2226                 VM_BUG_ON_PAGE(PageCompound(page), page);
2227                 VM_BUG_ON_PAGE(!PageAnon(page), page);
2228                 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2229
2230                 /*
2231                  * We can do it before isolate_lru_page because the
2232                  * page can't be freed from under us. NOTE: PG_lock
2233                  * is needed to serialize against split_huge_page
2234                  * when invoked from the VM.
2235                  */
2236                 if (!trylock_page(page))
2237                         goto out;
2238
2239                 /*
2240                  * cannot use mapcount: can't collapse if there's a gup pin.
2241                  * The page must only be referenced by the scanned process
2242                  * and page swap cache.
2243                  */
2244                 if (page_count(page) != 1 + !!PageSwapCache(page)) {
2245                         unlock_page(page);
2246                         goto out;
2247                 }
2248                 if (pte_write(pteval)) {
2249                         writable = true;
2250                 } else {
2251                         if (PageSwapCache(page) && !reuse_swap_page(page)) {
2252                                 unlock_page(page);
2253                                 goto out;
2254                         }
2255                         /*
2256                          * Page is not in the swap cache. It can be collapsed
2257                          * into a THP.
2258                          */
2259                 }
2260
2261                 /*
2262                  * Isolate the page to avoid collapsing an hugepage
2263                  * currently in use by the VM.
2264                  */
2265                 if (isolate_lru_page(page)) {
2266                         unlock_page(page);
2267                         goto out;
2268                 }
2269                 /* 0 stands for page_is_file_cache(page) == false */
2270                 inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2271                 VM_BUG_ON_PAGE(!PageLocked(page), page);
2272                 VM_BUG_ON_PAGE(PageLRU(page), page);
2273
2274                 /* If there is no mapped pte young don't collapse the page */
2275                 if (pte_young(pteval) || PageReferenced(page) ||
2276                     mmu_notifier_test_young(vma->vm_mm, address))
2277                         referenced = true;
2278         }
2279         if (likely(referenced && writable))
2280                 return 1;
2281 out:
2282         release_pte_pages(pte, _pte);
2283         return 0;
2284 }
2285
2286 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2287                                       struct vm_area_struct *vma,
2288                                       unsigned long address,
2289                                       spinlock_t *ptl)
2290 {
2291         pte_t *_pte;
2292         for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2293                 pte_t pteval = *_pte;
2294                 struct page *src_page;
2295
2296                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2297                         clear_user_highpage(page, address);
2298                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2299                         if (is_zero_pfn(pte_pfn(pteval))) {
2300                                 /*
2301                                  * ptl mostly unnecessary.
2302                                  */
2303                                 spin_lock(ptl);
2304                                 /*
2305                                  * paravirt calls inside pte_clear here are
2306                                  * superfluous.
2307                                  */
2308                                 pte_clear(vma->vm_mm, address, _pte);
2309                                 spin_unlock(ptl);
2310                         }
2311                 } else {
2312                         src_page = pte_page(pteval);
2313                         copy_user_highpage(page, src_page, address, vma);
2314                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
2315                         release_pte_page(src_page);
2316                         /*
2317                          * ptl mostly unnecessary, but preempt has to
2318                          * be disabled to update the per-cpu stats
2319                          * inside page_remove_rmap().
2320                          */
2321                         spin_lock(ptl);
2322                         /*
2323                          * paravirt calls inside pte_clear here are
2324                          * superfluous.
2325                          */
2326                         pte_clear(vma->vm_mm, address, _pte);
2327                         page_remove_rmap(src_page);
2328                         spin_unlock(ptl);
2329                         free_page_and_swap_cache(src_page);
2330                 }
2331
2332                 address += PAGE_SIZE;
2333                 page++;
2334         }
2335 }
2336
2337 static void khugepaged_alloc_sleep(void)
2338 {
2339         wait_event_freezable_timeout(khugepaged_wait, false,
2340                         msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2341 }
2342
2343 static int khugepaged_node_load[MAX_NUMNODES];
2344
2345 static bool khugepaged_scan_abort(int nid)
2346 {
2347         int i;
2348
2349         /*
2350          * If zone_reclaim_mode is disabled, then no extra effort is made to
2351          * allocate memory locally.
2352          */
2353         if (!zone_reclaim_mode)
2354                 return false;
2355
2356         /* If there is a count for this node already, it must be acceptable */
2357         if (khugepaged_node_load[nid])
2358                 return false;
2359
2360         for (i = 0; i < MAX_NUMNODES; i++) {
2361                 if (!khugepaged_node_load[i])
2362                         continue;
2363                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
2364                         return true;
2365         }
2366         return false;
2367 }
2368
2369 #ifdef CONFIG_NUMA
2370 static int khugepaged_find_target_node(void)
2371 {
2372         static int last_khugepaged_target_node = NUMA_NO_NODE;
2373         int nid, target_node = 0, max_value = 0;
2374
2375         /* find first node with max normal pages hit */
2376         for (nid = 0; nid < MAX_NUMNODES; nid++)
2377                 if (khugepaged_node_load[nid] > max_value) {
2378                         max_value = khugepaged_node_load[nid];
2379                         target_node = nid;
2380                 }
2381
2382         /* do some balance if several nodes have the same hit record */
2383         if (target_node <= last_khugepaged_target_node)
2384                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
2385                                 nid++)
2386                         if (max_value == khugepaged_node_load[nid]) {
2387                                 target_node = nid;
2388                                 break;
2389                         }
2390
2391         last_khugepaged_target_node = target_node;
2392         return target_node;
2393 }
2394
2395 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2396 {
2397         if (IS_ERR(*hpage)) {
2398                 if (!*wait)
2399                         return false;
2400
2401                 *wait = false;
2402                 *hpage = NULL;
2403                 khugepaged_alloc_sleep();
2404         } else if (*hpage) {
2405                 put_page(*hpage);
2406                 *hpage = NULL;
2407         }
2408
2409         return true;
2410 }
2411
2412 static struct page *
2413 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2414                        struct vm_area_struct *vma, unsigned long address,
2415                        int node)
2416 {
2417         VM_BUG_ON_PAGE(*hpage, *hpage);
2418
2419         /*
2420          * Before allocating the hugepage, release the mmap_sem read lock.
2421          * The allocation can take potentially a long time if it involves
2422          * sync compaction, and we do not need to hold the mmap_sem during
2423          * that. We will recheck the vma after taking it again in write mode.
2424          */
2425         up_read(&mm->mmap_sem);
2426
2427         *hpage = alloc_pages_exact_node(node, gfp, HPAGE_PMD_ORDER);
2428         if (unlikely(!*hpage)) {
2429                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2430                 *hpage = ERR_PTR(-ENOMEM);
2431                 return NULL;
2432         }
2433
2434         count_vm_event(THP_COLLAPSE_ALLOC);
2435         return *hpage;
2436 }
2437 #else
2438 static int khugepaged_find_target_node(void)
2439 {
2440         return 0;
2441 }
2442
2443 static inline struct page *alloc_hugepage(int defrag)
2444 {
2445         return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
2446                            HPAGE_PMD_ORDER);
2447 }
2448
2449 static struct page *khugepaged_alloc_hugepage(bool *wait)
2450 {
2451         struct page *hpage;
2452
2453         do {
2454                 hpage = alloc_hugepage(khugepaged_defrag());
2455                 if (!hpage) {
2456                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2457                         if (!*wait)
2458                                 return NULL;
2459
2460                         *wait = false;
2461                         khugepaged_alloc_sleep();
2462                 } else
2463                         count_vm_event(THP_COLLAPSE_ALLOC);
2464         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
2465
2466         return hpage;
2467 }
2468
2469 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2470 {
2471         if (!*hpage)
2472                 *hpage = khugepaged_alloc_hugepage(wait);
2473
2474         if (unlikely(!*hpage))
2475                 return false;
2476
2477         return true;
2478 }
2479
2480 static struct page *
2481 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2482                        struct vm_area_struct *vma, unsigned long address,
2483                        int node)
2484 {
2485         up_read(&mm->mmap_sem);
2486         VM_BUG_ON(!*hpage);
2487
2488         return  *hpage;
2489 }
2490 #endif
2491
2492 static bool hugepage_vma_check(struct vm_area_struct *vma)
2493 {
2494         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2495             (vma->vm_flags & VM_NOHUGEPAGE))
2496                 return false;
2497
2498         if (!vma->anon_vma || vma->vm_ops)
2499                 return false;
2500         if (is_vma_temporary_stack(vma))
2501                 return false;
2502         VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2503         return true;
2504 }
2505
2506 static void collapse_huge_page(struct mm_struct *mm,
2507                                    unsigned long address,
2508                                    struct page **hpage,
2509                                    struct vm_area_struct *vma,
2510                                    int node)
2511 {
2512         pmd_t *pmd, _pmd;
2513         pte_t *pte;
2514         pgtable_t pgtable;
2515         struct page *new_page;
2516         spinlock_t *pmd_ptl, *pte_ptl;
2517         int isolated;
2518         unsigned long hstart, hend;
2519         struct mem_cgroup *memcg;
2520         unsigned long mmun_start;       /* For mmu_notifiers */
2521         unsigned long mmun_end;         /* For mmu_notifiers */
2522         gfp_t gfp;
2523
2524         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2525
2526         /* Only allocate from the target node */
2527         gfp = alloc_hugepage_gfpmask(khugepaged_defrag(), __GFP_OTHER_NODE) |
2528                 __GFP_THISNODE;
2529
2530         /* release the mmap_sem read lock. */
2531         new_page = khugepaged_alloc_page(hpage, gfp, mm, vma, address, node);
2532         if (!new_page)
2533                 return;
2534
2535         if (unlikely(mem_cgroup_try_charge(new_page, mm,
2536                                            gfp, &memcg)))
2537                 return;
2538
2539         /*
2540          * Prevent all access to pagetables with the exception of
2541          * gup_fast later hanlded by the ptep_clear_flush and the VM
2542          * handled by the anon_vma lock + PG_lock.
2543          */
2544         down_write(&mm->mmap_sem);
2545         if (unlikely(khugepaged_test_exit(mm)))
2546                 goto out;
2547
2548         vma = find_vma(mm, address);
2549         if (!vma)
2550                 goto out;
2551         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2552         hend = vma->vm_end & HPAGE_PMD_MASK;
2553         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2554                 goto out;
2555         if (!hugepage_vma_check(vma))
2556                 goto out;
2557         pmd = mm_find_pmd(mm, address);
2558         if (!pmd)
2559                 goto out;
2560
2561         anon_vma_lock_write(vma->anon_vma);
2562
2563         pte = pte_offset_map(pmd, address);
2564         pte_ptl = pte_lockptr(mm, pmd);
2565
2566         mmun_start = address;
2567         mmun_end   = address + HPAGE_PMD_SIZE;
2568         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2569         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
2570         /*
2571          * After this gup_fast can't run anymore. This also removes
2572          * any huge TLB entry from the CPU so we won't allow
2573          * huge and small TLB entries for the same virtual address
2574          * to avoid the risk of CPU bugs in that area.
2575          */
2576         _pmd = pmdp_collapse_flush(vma, address, pmd);
2577         spin_unlock(pmd_ptl);
2578         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2579
2580         spin_lock(pte_ptl);
2581         isolated = __collapse_huge_page_isolate(vma, address, pte);
2582         spin_unlock(pte_ptl);
2583
2584         if (unlikely(!isolated)) {
2585                 pte_unmap(pte);
2586                 spin_lock(pmd_ptl);
2587                 BUG_ON(!pmd_none(*pmd));
2588                 /*
2589                  * We can only use set_pmd_at when establishing
2590                  * hugepmds and never for establishing regular pmds that
2591                  * points to regular pagetables. Use pmd_populate for that
2592                  */
2593                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2594                 spin_unlock(pmd_ptl);
2595                 anon_vma_unlock_write(vma->anon_vma);
2596                 goto out;
2597         }
2598
2599         /*
2600          * All pages are isolated and locked so anon_vma rmap
2601          * can't run anymore.
2602          */
2603         anon_vma_unlock_write(vma->anon_vma);
2604
2605         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
2606         pte_unmap(pte);
2607         __SetPageUptodate(new_page);
2608         pgtable = pmd_pgtable(_pmd);
2609
2610         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
2611         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
2612
2613         /*
2614          * spin_lock() below is not the equivalent of smp_wmb(), so
2615          * this is needed to avoid the copy_huge_page writes to become
2616          * visible after the set_pmd_at() write.
2617          */
2618         smp_wmb();
2619
2620         spin_lock(pmd_ptl);
2621         BUG_ON(!pmd_none(*pmd));
2622         page_add_new_anon_rmap(new_page, vma, address);
2623         mem_cgroup_commit_charge(new_page, memcg, false);
2624         lru_cache_add_active_or_unevictable(new_page, vma);
2625         pgtable_trans_huge_deposit(mm, pmd, pgtable);
2626         set_pmd_at(mm, address, pmd, _pmd);
2627         update_mmu_cache_pmd(vma, address, pmd);
2628         spin_unlock(pmd_ptl);
2629
2630         *hpage = NULL;
2631
2632         khugepaged_pages_collapsed++;
2633 out_up_write:
2634         up_write(&mm->mmap_sem);
2635         return;
2636
2637 out:
2638         mem_cgroup_cancel_charge(new_page, memcg);
2639         goto out_up_write;
2640 }
2641
2642 static int khugepaged_scan_pmd(struct mm_struct *mm,
2643                                struct vm_area_struct *vma,
2644                                unsigned long address,
2645                                struct page **hpage)
2646 {
2647         pmd_t *pmd;
2648         pte_t *pte, *_pte;
2649         int ret = 0, none_or_zero = 0;
2650         struct page *page;
2651         unsigned long _address;
2652         spinlock_t *ptl;
2653         int node = NUMA_NO_NODE;
2654         bool writable = false, referenced = false;
2655
2656         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2657
2658         pmd = mm_find_pmd(mm, address);
2659         if (!pmd)
2660                 goto out;
2661
2662         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
2663         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2664         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2665              _pte++, _address += PAGE_SIZE) {
2666                 pte_t pteval = *_pte;
2667                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2668                         if (!userfaultfd_armed(vma) &&
2669                             ++none_or_zero <= khugepaged_max_ptes_none)
2670                                 continue;
2671                         else
2672                                 goto out_unmap;
2673                 }
2674                 if (!pte_present(pteval))
2675                         goto out_unmap;
2676                 if (pte_write(pteval))
2677                         writable = true;
2678
2679                 page = vm_normal_page(vma, _address, pteval);
2680                 if (unlikely(!page))
2681                         goto out_unmap;
2682                 /*
2683                  * Record which node the original page is from and save this
2684                  * information to khugepaged_node_load[].
2685                  * Khupaged will allocate hugepage from the node has the max
2686                  * hit record.
2687                  */
2688                 node = page_to_nid(page);
2689                 if (khugepaged_scan_abort(node))
2690                         goto out_unmap;
2691                 khugepaged_node_load[node]++;
2692                 VM_BUG_ON_PAGE(PageCompound(page), page);
2693                 if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2694                         goto out_unmap;
2695                 /*
2696                  * cannot use mapcount: can't collapse if there's a gup pin.
2697                  * The page must only be referenced by the scanned process
2698                  * and page swap cache.
2699                  */
2700                 if (page_count(page) != 1 + !!PageSwapCache(page))
2701                         goto out_unmap;
2702                 if (pte_young(pteval) || PageReferenced(page) ||
2703                     mmu_notifier_test_young(vma->vm_mm, address))
2704                         referenced = true;
2705         }
2706         if (referenced && writable)
2707                 ret = 1;
2708 out_unmap:
2709         pte_unmap_unlock(pte, ptl);
2710         if (ret) {
2711                 node = khugepaged_find_target_node();
2712                 /* collapse_huge_page will return with the mmap_sem released */
2713                 collapse_huge_page(mm, address, hpage, vma, node);
2714         }
2715 out:
2716         return ret;
2717 }
2718
2719 static void collect_mm_slot(struct mm_slot *mm_slot)
2720 {
2721         struct mm_struct *mm = mm_slot->mm;
2722
2723         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2724
2725         if (khugepaged_test_exit(mm)) {
2726                 /* free mm_slot */
2727                 hash_del(&mm_slot->hash);
2728                 list_del(&mm_slot->mm_node);
2729
2730                 /*
2731                  * Not strictly needed because the mm exited already.
2732                  *
2733                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2734                  */
2735
2736                 /* khugepaged_mm_lock actually not necessary for the below */
2737                 free_mm_slot(mm_slot);
2738                 mmdrop(mm);
2739         }
2740 }
2741
2742 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2743                                             struct page **hpage)
2744         __releases(&khugepaged_mm_lock)
2745         __acquires(&khugepaged_mm_lock)
2746 {
2747         struct mm_slot *mm_slot;
2748         struct mm_struct *mm;
2749         struct vm_area_struct *vma;
2750         int progress = 0;
2751
2752         VM_BUG_ON(!pages);
2753         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2754
2755         if (khugepaged_scan.mm_slot)
2756                 mm_slot = khugepaged_scan.mm_slot;
2757         else {
2758                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2759                                      struct mm_slot, mm_node);
2760                 khugepaged_scan.address = 0;
2761                 khugepaged_scan.mm_slot = mm_slot;
2762         }
2763         spin_unlock(&khugepaged_mm_lock);
2764
2765         mm = mm_slot->mm;
2766         down_read(&mm->mmap_sem);
2767         if (unlikely(khugepaged_test_exit(mm)))
2768                 vma = NULL;
2769         else
2770                 vma = find_vma(mm, khugepaged_scan.address);
2771
2772         progress++;
2773         for (; vma; vma = vma->vm_next) {
2774                 unsigned long hstart, hend;
2775
2776                 cond_resched();
2777                 if (unlikely(khugepaged_test_exit(mm))) {
2778                         progress++;
2779                         break;
2780                 }
2781                 if (!hugepage_vma_check(vma)) {
2782 skip:
2783                         progress++;
2784                         continue;
2785                 }
2786                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2787                 hend = vma->vm_end & HPAGE_PMD_MASK;
2788                 if (hstart >= hend)
2789                         goto skip;
2790                 if (khugepaged_scan.address > hend)
2791                         goto skip;
2792                 if (khugepaged_scan.address < hstart)
2793                         khugepaged_scan.address = hstart;
2794                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2795
2796                 while (khugepaged_scan.address < hend) {
2797                         int ret;
2798                         cond_resched();
2799                         if (unlikely(khugepaged_test_exit(mm)))
2800                                 goto breakouterloop;
2801
2802                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2803                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2804                                   hend);
2805                         ret = khugepaged_scan_pmd(mm, vma,
2806                                                   khugepaged_scan.address,
2807                                                   hpage);
2808                         /* move to next address */
2809                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2810                         progress += HPAGE_PMD_NR;
2811                         if (ret)
2812                                 /* we released mmap_sem so break loop */
2813                                 goto breakouterloop_mmap_sem;
2814                         if (progress >= pages)
2815                                 goto breakouterloop;
2816                 }
2817         }
2818 breakouterloop:
2819         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2820 breakouterloop_mmap_sem:
2821
2822         spin_lock(&khugepaged_mm_lock);
2823         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2824         /*
2825          * Release the current mm_slot if this mm is about to die, or
2826          * if we scanned all vmas of this mm.
2827          */
2828         if (khugepaged_test_exit(mm) || !vma) {
2829                 /*
2830                  * Make sure that if mm_users is reaching zero while
2831                  * khugepaged runs here, khugepaged_exit will find
2832                  * mm_slot not pointing to the exiting mm.
2833                  */
2834                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2835                         khugepaged_scan.mm_slot = list_entry(
2836                                 mm_slot->mm_node.next,
2837                                 struct mm_slot, mm_node);
2838                         khugepaged_scan.address = 0;
2839                 } else {
2840                         khugepaged_scan.mm_slot = NULL;
2841                         khugepaged_full_scans++;
2842                 }
2843
2844                 collect_mm_slot(mm_slot);
2845         }
2846
2847         return progress;
2848 }
2849
2850 static int khugepaged_has_work(void)
2851 {
2852         return !list_empty(&khugepaged_scan.mm_head) &&
2853                 khugepaged_enabled();
2854 }
2855
2856 static int khugepaged_wait_event(void)
2857 {
2858         return !list_empty(&khugepaged_scan.mm_head) ||
2859                 kthread_should_stop();
2860 }
2861
2862 static void khugepaged_do_scan(void)
2863 {
2864         struct page *hpage = NULL;
2865         unsigned int progress = 0, pass_through_head = 0;
2866         unsigned int pages = khugepaged_pages_to_scan;
2867         bool wait = true;
2868
2869         barrier(); /* write khugepaged_pages_to_scan to local stack */
2870
2871         while (progress < pages) {
2872                 if (!khugepaged_prealloc_page(&hpage, &wait))
2873                         break;
2874
2875                 cond_resched();
2876
2877                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2878                         break;
2879
2880                 spin_lock(&khugepaged_mm_lock);
2881                 if (!khugepaged_scan.mm_slot)
2882                         pass_through_head++;
2883                 if (khugepaged_has_work() &&
2884                     pass_through_head < 2)
2885                         progress += khugepaged_scan_mm_slot(pages - progress,
2886                                                             &hpage);
2887                 else
2888                         progress = pages;
2889                 spin_unlock(&khugepaged_mm_lock);
2890         }
2891
2892         if (!IS_ERR_OR_NULL(hpage))
2893                 put_page(hpage);
2894 }
2895
2896 static void khugepaged_wait_work(void)
2897 {
2898         if (khugepaged_has_work()) {
2899                 if (!khugepaged_scan_sleep_millisecs)
2900                         return;
2901
2902                 wait_event_freezable_timeout(khugepaged_wait,
2903                                              kthread_should_stop(),
2904                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2905                 return;
2906         }
2907
2908         if (khugepaged_enabled())
2909                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2910 }
2911
2912 static int khugepaged(void *none)
2913 {
2914         struct mm_slot *mm_slot;
2915
2916         set_freezable();
2917         set_user_nice(current, MAX_NICE);
2918
2919         while (!kthread_should_stop()) {
2920                 khugepaged_do_scan();
2921                 khugepaged_wait_work();
2922         }
2923
2924         spin_lock(&khugepaged_mm_lock);
2925         mm_slot = khugepaged_scan.mm_slot;
2926         khugepaged_scan.mm_slot = NULL;
2927         if (mm_slot)
2928                 collect_mm_slot(mm_slot);
2929         spin_unlock(&khugepaged_mm_lock);
2930         return 0;
2931 }
2932
2933 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2934                 unsigned long haddr, pmd_t *pmd)
2935 {
2936         struct mm_struct *mm = vma->vm_mm;
2937         pgtable_t pgtable;
2938         pmd_t _pmd;
2939         int i;
2940
2941         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
2942         /* leave pmd empty until pte is filled */
2943
2944         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2945         pmd_populate(mm, &_pmd, pgtable);
2946
2947         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2948                 pte_t *pte, entry;
2949                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2950                 entry = pte_mkspecial(entry);
2951                 pte = pte_offset_map(&_pmd, haddr);
2952                 VM_BUG_ON(!pte_none(*pte));
2953                 set_pte_at(mm, haddr, pte, entry);
2954                 pte_unmap(pte);
2955         }
2956         smp_wmb(); /* make pte visible before pmd */
2957         pmd_populate(mm, pmd, pgtable);
2958         put_huge_zero_page();
2959 }
2960
2961 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2962                 pmd_t *pmd)
2963 {
2964         spinlock_t *ptl;
2965         struct page *page = NULL;
2966         struct mm_struct *mm = vma->vm_mm;
2967         unsigned long haddr = address & HPAGE_PMD_MASK;
2968         unsigned long mmun_start;       /* For mmu_notifiers */
2969         unsigned long mmun_end;         /* For mmu_notifiers */
2970
2971         BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2972
2973         mmun_start = haddr;
2974         mmun_end   = haddr + HPAGE_PMD_SIZE;
2975 again:
2976         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2977         ptl = pmd_lock(mm, pmd);
2978         if (unlikely(!pmd_trans_huge(*pmd)))
2979                 goto unlock;
2980         if (vma_is_dax(vma)) {
2981                 pmdp_huge_clear_flush(vma, haddr, pmd);
2982         } else if (is_huge_zero_pmd(*pmd)) {
2983                 __split_huge_zero_page_pmd(vma, haddr, pmd);
2984         } else {
2985                 page = pmd_page(*pmd);
2986                 VM_BUG_ON_PAGE(!page_count(page), page);
2987                 get_page(page);
2988         }
2989  unlock:
2990         spin_unlock(ptl);
2991         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2992
2993         if (!page)
2994                 return;
2995
2996         split_huge_page(page);
2997         put_page(page);
2998
2999         /*
3000          * We don't always have down_write of mmap_sem here: a racing
3001          * do_huge_pmd_wp_page() might have copied-on-write to another
3002          * huge page before our split_huge_page() got the anon_vma lock.
3003          */
3004         if (unlikely(pmd_trans_huge(*pmd)))
3005                 goto again;
3006 }
3007
3008 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
3009                 pmd_t *pmd)
3010 {
3011         struct vm_area_struct *vma;
3012
3013         vma = find_vma(mm, address);
3014         BUG_ON(vma == NULL);
3015         split_huge_page_pmd(vma, address, pmd);
3016 }
3017
3018 static void split_huge_page_address(struct mm_struct *mm,
3019                                     unsigned long address)
3020 {
3021         pgd_t *pgd;
3022         pud_t *pud;
3023         pmd_t *pmd;
3024
3025         VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
3026
3027         pgd = pgd_offset(mm, address);
3028         if (!pgd_present(*pgd))
3029                 return;
3030
3031         pud = pud_offset(pgd, address);
3032         if (!pud_present(*pud))
3033                 return;
3034
3035         pmd = pmd_offset(pud, address);
3036         if (!pmd_present(*pmd))
3037                 return;
3038         /*
3039          * Caller holds the mmap_sem write mode, so a huge pmd cannot
3040          * materialize from under us.
3041          */
3042         split_huge_page_pmd_mm(mm, address, pmd);
3043 }
3044
3045 void vma_adjust_trans_huge(struct vm_area_struct *vma,
3046                              unsigned long start,
3047                              unsigned long end,
3048                              long adjust_next)
3049 {
3050         /*
3051          * If the new start address isn't hpage aligned and it could
3052          * previously contain an hugepage: check if we need to split
3053          * an huge pmd.
3054          */
3055         if (start & ~HPAGE_PMD_MASK &&
3056             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
3057             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
3058                 split_huge_page_address(vma->vm_mm, start);
3059
3060         /*
3061          * If the new end address isn't hpage aligned and it could
3062          * previously contain an hugepage: check if we need to split
3063          * an huge pmd.
3064          */
3065         if (end & ~HPAGE_PMD_MASK &&
3066             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
3067             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
3068                 split_huge_page_address(vma->vm_mm, end);
3069
3070         /*
3071          * If we're also updating the vma->vm_next->vm_start, if the new
3072          * vm_next->vm_start isn't page aligned and it could previously
3073          * contain an hugepage: check if we need to split an huge pmd.
3074          */
3075         if (adjust_next > 0) {
3076                 struct vm_area_struct *next = vma->vm_next;
3077                 unsigned long nstart = next->vm_start;
3078                 nstart += adjust_next << PAGE_SHIFT;
3079                 if (nstart & ~HPAGE_PMD_MASK &&
3080                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
3081                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
3082                         split_huge_page_address(next->vm_mm, nstart);
3083         }
3084 }