mm: catch memory commitment underflow

Print a warning (if CONFIG_DEBUG_VM=y) when memory commitment becomes
too negative.

This shouldn't happen any more - the previous two patches fixed the
committed_as underflow issues.

[akpm@linux-foundation.org: use VM_WARN_ONCE, per Dave]
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 129b847d30cc35c8724cee63e924f69faaf542c6..64c9d736155c7a546e6d133426a0861a63688ead 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -31,6 +31,7 @@
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
 #include <linux/mmu_notifier.h>
+#include <linux/mmdebug.h>
 #include <linux/perf_event.h>
 #include <linux/audit.h>
 #include <linux/khugepaged.h>
@@ -134,6 +135,10 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 {
        unsigned long free, allowed, reserve;
 
+       VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
+                       -(s64)vm_committed_as_batch * num_online_cpus(),
+                       "memory commitment underflow");
+
        vm_acct_memory(pages);
 
        /*