drivers/md/persistent-data/dm-btree-remove.c

   1 /*
   2  * Copyright (C) 2011 Red Hat, Inc.
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-btree.h"
   8 #include "dm-btree-internal.h"
   9 #include "dm-transaction-manager.h"
  10
  11 #include <linux/export.h>
  12
  13 /*
  14  * Removing an entry from a btree
  15  * ==============================
  16  *
  17  * A very important constraint for our btree is that no node, except the
  18  * root, may have fewer than a certain number of entries.
  19  * (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
  20  *
  21  * Ensuring this is complicated by the way we want to only ever hold the
  22  * locks on 2 nodes concurrently, and only change nodes in a top to bottom
  23  * fashion.
  24  *
  25  * Each node may have a left or right sibling.  When decending the spine,
  26  * if a node contains only MIN_ENTRIES then we try and increase this to at
  27  * least MIN_ENTRIES + 1.  We do this in the following ways:
  28  *
  29  * [A] No siblings => this can only happen if the node is the root, in which
  30  *     case we copy the childs contents over the root.
  31  *
  32  * [B] No left sibling
  33  *     ==> rebalance(node, right sibling)
  34  *
  35  * [C] No right sibling
  36  *     ==> rebalance(left sibling, node)
  37  *
  38  * [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
  39  *     ==> delete node adding it's contents to left and right
  40  *
  41  * [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
  42  *     ==> rebalance(left, node, right)
  43  *
  44  * After these operations it's possible that the our original node no
  45  * longer contains the desired sub tree.  For this reason this rebalancing
  46  * is performed on the children of the current node.  This also avoids
  47  * having a special case for the root.
  48  *
  49  * Once this rebalancing has occurred we can then step into the child node
  50  * for internal nodes.  Or delete the entry for leaf nodes.
  51  */
  52
  53 /*
  54  * Some little utilities for moving node data around.
  55  */
  56 static void node_shift(struct btree_node *n, int shift)
  57 {
  58         uint32_t nr_entries = le32_to_cpu(n->header.nr_entries);
  59         uint32_t value_size = le32_to_cpu(n->header.value_size);
  60
  61         if (shift < 0) {
  62                 shift = -shift;
  63                 BUG_ON(shift > nr_entries);
  64                 BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift));
  65                 memmove(key_ptr(n, 0),
  66                         key_ptr(n, shift),
  67                         (nr_entries - shift) * sizeof(__le64));
  68                 memmove(value_ptr(n, 0),
  69                         value_ptr(n, shift),
  70                         (nr_entries - shift) * value_size);
  71         } else {
  72                 BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
  73                 memmove(key_ptr(n, shift),
  74                         key_ptr(n, 0),
  75                         nr_entries * sizeof(__le64));
  76                 memmove(value_ptr(n, shift),
  77                         value_ptr(n, 0),
  78                         nr_entries * value_size);
  79         }
  80 }
  81
  82 static void node_copy(struct btree_node *left, struct btree_node *right, int shift)
  83 {
  84         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
  85         uint32_t value_size = le32_to_cpu(left->header.value_size);
  86         BUG_ON(value_size != le32_to_cpu(right->header.value_size));
  87
  88         if (shift < 0) {
  89                 shift = -shift;
  90                 BUG_ON(nr_left + shift > le32_to_cpu(left->header.max_entries));
  91                 memcpy(key_ptr(left, nr_left),
  92                        key_ptr(right, 0),
  93                        shift * sizeof(__le64));
  94                 memcpy(value_ptr(left, nr_left),
  95                        value_ptr(right, 0),
  96                        shift * value_size);
  97         } else {
  98                 BUG_ON(shift > le32_to_cpu(right->header.max_entries));
  99                 memcpy(key_ptr(right, 0),
 100                        key_ptr(left, nr_left - shift),
 101                        shift * sizeof(__le64));
 102                 memcpy(value_ptr(right, 0),
 103                        value_ptr(left, nr_left - shift),
 104                        shift * value_size);
 105         }
 106 }
 107
 108 /*
 109  * Delete a specific entry from a leaf node.
 110  */
 111 static void delete_at(struct btree_node *n, unsigned index)
 112 {
 113         unsigned nr_entries = le32_to_cpu(n->header.nr_entries);
 114         unsigned nr_to_copy = nr_entries - (index + 1);
 115         uint32_t value_size = le32_to_cpu(n->header.value_size);
 116         BUG_ON(index >= nr_entries);
 117
 118         if (nr_to_copy) {
 119                 memmove(key_ptr(n, index),
 120                         key_ptr(n, index + 1),
 121                         nr_to_copy * sizeof(__le64));
 122
 123                 memmove(value_ptr(n, index),
 124                         value_ptr(n, index + 1),
 125                         nr_to_copy * value_size);
 126         }
 127
 128         n->header.nr_entries = cpu_to_le32(nr_entries - 1);
 129 }
 130
 131 static unsigned merge_threshold(struct btree_node *n)
 132 {
 133         return le32_to_cpu(n->header.max_entries) / 3;
 134 }
 135
 136 struct child {
 137         unsigned index;
 138         struct dm_block *block;
 139         struct btree_node *n;
 140 };
 141
 142 static int init_child(struct dm_btree_info *info, struct dm_btree_value_type *vt,
 143                       struct btree_node *parent,
 144                       unsigned index, struct child *result)
 145 {
 146         int r, inc;
 147         dm_block_t root;
 148
 149         result->index = index;
 150         root = value64(parent, index);
 151
 152         r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
 153                                &result->block, &inc);
 154         if (r)
 155                 return r;
 156
 157         result->n = dm_block_data(result->block);
 158
 159         if (inc)
 160                 inc_children(info->tm, result->n, vt);
 161
 162         *((__le64 *) value_ptr(parent, index)) =
 163                 cpu_to_le64(dm_block_location(result->block));
 164
 165         return 0;
 166 }
 167
 168 static void exit_child(struct dm_btree_info *info, struct child *c)
 169 {
 170         dm_tm_unlock(info->tm, c->block);
 171 }
 172
 173 static void shift(struct btree_node *left, struct btree_node *right, int count)
 174 {
 175         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 176         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 177         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 178         uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
 179
 180         BUG_ON(max_entries != r_max_entries);
 181         BUG_ON(nr_left - count > max_entries);
 182         BUG_ON(nr_right + count > max_entries);
 183
 184         if (!count)
 185                 return;
 186
 187         if (count > 0) {
 188                 node_shift(right, count);
 189                 node_copy(left, right, count);
 190         } else {
 191                 node_copy(left, right, count);
 192                 node_shift(right, count);
 193         }
 194
 195         left->header.nr_entries = cpu_to_le32(nr_left - count);
 196         right->header.nr_entries = cpu_to_le32(nr_right + count);
 197 }
 198
 199 static void __rebalance2(struct dm_btree_info *info, struct btree_node *parent,
 200                          struct child *l, struct child *r)
 201 {
 202         struct btree_node *left = l->n;
 203         struct btree_node *right = r->n;
 204         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 205         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 206         unsigned threshold = 2 * merge_threshold(left) + 1;
 207
 208         if (nr_left + nr_right < threshold) {
 209                 /*
 210                  * Merge
 211                  */
 212                 node_copy(left, right, -nr_right);
 213                 left->header.nr_entries = cpu_to_le32(nr_left + nr_right);
 214                 delete_at(parent, r->index);
 215
 216                 /*
 217                  * We need to decrement the right block, but not it's
 218                  * children, since they're still referenced by left.
 219                  */
 220                 dm_tm_dec(info->tm, dm_block_location(r->block));
 221         } else {
 222                 /*
 223                  * Rebalance.
 224                  */
 225                 unsigned target_left = (nr_left + nr_right) / 2;
 226                 shift(left, right, nr_left - target_left);
 227                 *key_ptr(parent, r->index) = right->keys[0];
 228         }
 229 }
 230
 231 static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
 232                       struct dm_btree_value_type *vt, unsigned left_index)
 233 {
 234         int r;
 235         struct btree_node *parent;
 236         struct child left, right;
 237
 238         parent = dm_block_data(shadow_current(s));
 239
 240         r = init_child(info, vt, parent, left_index, &left);
 241         if (r)
 242                 return r;
 243
 244         r = init_child(info, vt, parent, left_index + 1, &right);
 245         if (r) {
 246                 exit_child(info, &left);
 247                 return r;
 248         }
 249
 250         __rebalance2(info, parent, &left, &right);
 251
 252         exit_child(info, &left);
 253         exit_child(info, &right);
 254
 255         return 0;
 256 }
 257
 258 /*
 259  * We dump as many entries from center as possible into left, then the rest
 260  * in right, then rebalance2.  This wastes some cpu, but I want something
 261  * simple atm.
 262  */
 263 static void delete_center_node(struct dm_btree_info *info, struct btree_node *parent,
 264                                struct child *l, struct child *c, struct child *r,
 265                                struct btree_node *left, struct btree_node *center, struct btree_node *right,
 266                                uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 267 {
 268         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 269         unsigned shift = min(max_entries - nr_left, nr_center);
 270
 271         BUG_ON(nr_left + shift > max_entries);
 272         node_copy(left, center, -shift);
 273         left->header.nr_entries = cpu_to_le32(nr_left + shift);
 274
 275         if (shift != nr_center) {
 276                 shift = nr_center - shift;
 277                 BUG_ON((nr_right + shift) > max_entries);
 278                 node_shift(right, shift);
 279                 node_copy(center, right, shift);
 280                 right->header.nr_entries = cpu_to_le32(nr_right + shift);
 281         }
 282         *key_ptr(parent, r->index) = right->keys[0];
 283
 284         delete_at(parent, c->index);
 285         r->index--;
 286
 287         dm_tm_dec(info->tm, dm_block_location(c->block));
 288         __rebalance2(info, parent, l, r);
 289 }
 290
 291 /*
 292  * Redistributes entries among 3 sibling nodes.
 293  */
 294 static void redistribute3(struct dm_btree_info *info, struct btree_node *parent,
 295                           struct child *l, struct child *c, struct child *r,
 296                           struct btree_node *left, struct btree_node *center, struct btree_node *right,
 297                           uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
 298 {
 299         int s;
 300         uint32_t max_entries = le32_to_cpu(left->header.max_entries);
 301         unsigned target = (nr_left + nr_center + nr_right) / 3;
 302         BUG_ON(target > max_entries);
 303
 304         if (nr_left < nr_right) {
 305                 s = nr_left - target;
 306
 307                 if (s < 0 && nr_center < -s) {
 308                         /* not enough in central node */
 309                         shift(left, center, -nr_center);
 310                         s += nr_center;
 311                         shift(left, right, s);
 312                         nr_right += s;
 313                 } else
 314                         shift(left, center, s);
 315
 316                 shift(center, right, target - nr_right);
 317
 318         } else {
 319                 s = target - nr_right;
 320                 if (s > 0 && nr_center < s) {
 321                         /* not enough in central node */
 322                         shift(center, right, nr_center);
 323                         s -= nr_center;
 324                         shift(left, right, s);
 325                         nr_left -= s;
 326                 } else
 327                         shift(center, right, s);
 328
 329                 shift(left, center, nr_left - target);
 330         }
 331
 332         *key_ptr(parent, c->index) = center->keys[0];
 333         *key_ptr(parent, r->index) = right->keys[0];
 334 }
 335
 336 static void __rebalance3(struct dm_btree_info *info, struct btree_node *parent,
 337                          struct child *l, struct child *c, struct child *r)
 338 {
 339         struct btree_node *left = l->n;
 340         struct btree_node *center = c->n;
 341         struct btree_node *right = r->n;
 342
 343         uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
 344         uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
 345         uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
 346
 347         unsigned threshold = merge_threshold(left) * 4 + 1;
 348
 349         BUG_ON(left->header.max_entries != center->header.max_entries);
 350         BUG_ON(center->header.max_entries != right->header.max_entries);
 351
 352         if ((nr_left + nr_center + nr_right) < threshold)
 353                 delete_center_node(info, parent, l, c, r, left, center, right,
 354                                    nr_left, nr_center, nr_right);
 355         else
 356                 redistribute3(info, parent, l, c, r, left, center, right,
 357                               nr_left, nr_center, nr_right);
 358 }
 359
 360 static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
 361                       struct dm_btree_value_type *vt, unsigned left_index)
 362 {
 363         int r;
 364         struct btree_node *parent = dm_block_data(shadow_current(s));
 365         struct child left, center, right;
 366
 367         /*
 368          * FIXME: fill out an array?
 369          */
 370         r = init_child(info, vt, parent, left_index, &left);
 371         if (r)
 372                 return r;
 373
 374         r = init_child(info, vt, parent, left_index + 1, &center);
 375         if (r) {
 376                 exit_child(info, &left);
 377                 return r;
 378         }
 379
 380         r = init_child(info, vt, parent, left_index + 2, &right);
 381         if (r) {
 382                 exit_child(info, &left);
 383                 exit_child(info, &center);
 384                 return r;
 385         }
 386
 387         __rebalance3(info, parent, &left, &center, &right);
 388
 389         exit_child(info, &left);
 390         exit_child(info, &center);
 391         exit_child(info, &right);
 392
 393         return 0;
 394 }
 395
 396 static int rebalance_children(struct shadow_spine *s,
 397                               struct dm_btree_info *info,
 398                               struct dm_btree_value_type *vt, uint64_t key)
 399 {
 400         int i, r, has_left_sibling, has_right_sibling;
 401         struct btree_node *n;
 402
 403         n = dm_block_data(shadow_current(s));
 404
 405         if (le32_to_cpu(n->header.nr_entries) == 1) {
 406                 struct dm_block *child;
 407                 dm_block_t b = value64(n, 0);
 408
 409                 r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
 410                 if (r)
 411                         return r;
 412
 413                 memcpy(n, dm_block_data(child),
 414                        dm_bm_block_size(dm_tm_get_bm(info->tm)));
 415                 dm_tm_unlock(info->tm, child);
 416
 417                 dm_tm_dec(info->tm, dm_block_location(child));
 418                 return 0;
 419         }
 420
 421         i = lower_bound(n, key);
 422         if (i < 0)
 423                 return -ENODATA;
 424
 425         has_left_sibling = i > 0;
 426         has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);
 427
 428         if (!has_left_sibling)
 429                 r = rebalance2(s, info, vt, i);
 430
 431         else if (!has_right_sibling)
 432                 r = rebalance2(s, info, vt, i - 1);
 433
 434         else
 435                 r = rebalance3(s, info, vt, i - 1);
 436
 437         return r;
 438 }
 439
 440 static int do_leaf(struct btree_node *n, uint64_t key, unsigned *index)
 441 {
 442         int i = lower_bound(n, key);
 443
 444         if ((i < 0) ||
 445             (i >= le32_to_cpu(n->header.nr_entries)) ||
 446             (le64_to_cpu(n->keys[i]) != key))
 447                 return -ENODATA;
 448
 449         *index = i;
 450
 451         return 0;
 452 }
 453
 454 /*
 455  * Prepares for removal from one level of the hierarchy.  The caller must
 456  * call delete_at() to remove the entry at index.
 457  */
 458 static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
 459                       struct dm_btree_value_type *vt, dm_block_t root,
 460                       uint64_t key, unsigned *index)
 461 {
 462         int i = *index, r;
 463         struct btree_node *n;
 464
 465         for (;;) {
 466                 r = shadow_step(s, root, vt);
 467                 if (r < 0)
 468                         break;
 469
 470                 /*
 471                  * We have to patch up the parent node, ugly, but I don't
 472                  * see a way to do this automatically as part of the spine
 473                  * op.
 474                  */
 475                 if (shadow_has_parent(s)) {
 476                         __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
 477                         memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
 478                                &location, sizeof(__le64));
 479                 }
 480
 481                 n = dm_block_data(shadow_current(s));
 482
 483                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 484                         return do_leaf(n, key, index);
 485
 486                 r = rebalance_children(s, info, vt, key);
 487                 if (r)
 488                         break;
 489
 490                 n = dm_block_data(shadow_current(s));
 491                 if (le32_to_cpu(n->header.flags) & LEAF_NODE)
 492                         return do_leaf(n, key, index);
 493
 494                 i = lower_bound(n, key);
 495
 496                 /*
 497                  * We know the key is present, or else
 498                  * rebalance_children would have returned
 499                  * -ENODATA
 500                  */
 501                 root = value64(n, i);
 502         }
 503
 504         return r;
 505 }
 506
 507 int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
 508                     uint64_t *keys, dm_block_t *new_root)
 509 {
 510         unsigned level, last_level = info->levels - 1;
 511         int index = 0, r = 0;
 512         struct shadow_spine spine;
 513         struct btree_node *n;
 514         struct dm_btree_value_type le64_vt;
 515
 516         init_le64_type(info->tm, &le64_vt);
 517         init_shadow_spine(&spine, info);
 518         for (level = 0; level < info->levels; level++) {
 519                 r = remove_raw(&spine, info,
 520                                (level == last_level ?
 521                                 &info->value_type : &le64_vt),
 522                                root, keys[level], (unsigned *)&index);
 523                 if (r < 0)
 524                         break;
 525
 526                 n = dm_block_data(shadow_current(&spine));
 527                 if (level != last_level) {
 528                         root = value64(n, index);
 529                         continue;
 530                 }
 531
 532                 BUG_ON(index < 0 || index >= le32_to_cpu(n->header.nr_entries));
 533
 534                 if (info->value_type.dec)
 535                         info->value_type.dec(info->value_type.context,
 536                                              value_ptr(n, index));
 537
 538                 delete_at(n, index);
 539         }
 540
 541         *new_root = shadow_root(&spine);
 542         exit_shadow_spine(&spine);
 543
 544         return r;
 545 }
 546 EXPORT_SYMBOL_GPL(dm_btree_remove);
 547
 548 /*----------------------------------------------------------------*/
 549
 550 static int remove_nearest(struct shadow_spine *s, struct dm_btree_info *info,
 551                           struct dm_btree_value_type *vt, dm_block_t root,
 552                           uint64_t key, int *index)
 553 {
 554         int i = *index, r;
 555         struct btree_node *n;
 556
 557         for (;;) {
 558                 r = shadow_step(s, root, vt);
 559                 if (r < 0)
 560                         break;
 561
 562                 /*
 563                  * We have to patch up the parent node, ugly, but I don't
 564                  * see a way to do this automatically as part of the spine
 565                  * op.
 566                  */
 567                 if (shadow_has_parent(s)) {
 568                         __le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
 569                         memcpy(value_ptr(dm_block_data(shadow_parent(s)), i),
 570                                &location, sizeof(__le64));
 571                 }
 572
 573                 n = dm_block_data(shadow_current(s));
 574
 575                 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
 576                         *index = lower_bound(n, key);
 577                         return 0;
 578                 }
 579
 580                 r = rebalance_children(s, info, vt, key);
 581                 if (r)
 582                         break;
 583
 584                 n = dm_block_data(shadow_current(s));
 585                 if (le32_to_cpu(n->header.flags) & LEAF_NODE) {
 586                         *index = lower_bound(n, key);
 587                         return 0;
 588                 }
 589
 590                 i = lower_bound(n, key);
 591
 592                 /*
 593                  * We know the key is present, or else
 594                  * rebalance_children would have returned
 595                  * -ENODATA
 596                  */
 597                 root = value64(n, i);
 598         }
 599
 600         return r;
 601 }
 602
 603 static int remove_one(struct dm_btree_info *info, dm_block_t root,
 604                       uint64_t *keys, uint64_t end_key,
 605                       dm_block_t *new_root, unsigned *nr_removed)
 606 {
 607         unsigned level, last_level = info->levels - 1;
 608         int index = 0, r = 0;
 609         struct shadow_spine spine;
 610         struct btree_node *n;
 611         struct dm_btree_value_type le64_vt;
 612         uint64_t k;
 613
 614         init_le64_type(info->tm, &le64_vt);
 615         init_shadow_spine(&spine, info);
 616         for (level = 0; level < last_level; level++) {
 617                 r = remove_raw(&spine, info, &le64_vt,
 618                                root, keys[level], (unsigned *) &index);
 619                 if (r < 0)
 620                         goto out;
 621
 622                 n = dm_block_data(shadow_current(&spine));
 623                 root = value64(n, index);
 624         }
 625
 626         r = remove_nearest(&spine, info, &info->value_type,
 627                            root, keys[last_level], &index);
 628         if (r < 0)
 629                 goto out;
 630
 631         n = dm_block_data(shadow_current(&spine));
 632
 633         if (index < 0)
 634                 index = 0;
 635
 636         if (index >= le32_to_cpu(n->header.nr_entries)) {
 637                 r = -ENODATA;
 638                 goto out;
 639         }
 640
 641         k = le64_to_cpu(n->keys[index]);
 642         if (k >= keys[last_level] && k < end_key) {
 643                 if (info->value_type.dec)
 644                         info->value_type.dec(info->value_type.context,
 645                                              value_ptr(n, index));
 646
 647                 delete_at(n, index);
 648                 keys[last_level] = k + 1ull;
 649
 650         } else
 651                 r = -ENODATA;
 652
 653 out:
 654         *new_root = shadow_root(&spine);
 655         exit_shadow_spine(&spine);
 656
 657         return r;
 658 }
 659
 660 int dm_btree_remove_leaves(struct dm_btree_info *info, dm_block_t root,
 661                            uint64_t *first_key, uint64_t end_key,
 662                            dm_block_t *new_root, unsigned *nr_removed)
 663 {
 664         int r;
 665
 666         *nr_removed = 0;
 667         do {
 668                 r = remove_one(info, root, first_key, end_key, &root, nr_removed);
 669                 if (!r)
 670                         (*nr_removed)++;
 671         } while (!r);
 672
 673         *new_root = root;
 674         return r == -ENODATA ? 0 : r;
 675 }
 676 EXPORT_SYMBOL_GPL(dm_btree_remove_leaves);