mm: fix Committed_AS underflow on large NR_CPUS environment
The Committed_AS field can underflow in certain situations:
> # while true; do cat /proc/meminfo | grep _AS; sleep 1; done | uniq -c
> 1 Committed_AS: 18446744073709323392 kB
> 11 Committed_AS: 18446744073709455488 kB
> 6 Committed_AS: 35136 kB
> 5 Committed_AS: 18446744073709454400 kB
> 7 Committed_AS: 35904 kB
> 3 Committed_AS: 18446744073709453248 kB
> 2 Committed_AS: 34752 kB
> 9 Committed_AS: 18446744073709453248 kB
> 8 Committed_AS: 34752 kB
> 3 Committed_AS: 18446744073709320960 kB
> 7 Committed_AS: 18446744073709454080 kB
> 3 Committed_AS: 18446744073709320960 kB
> 5 Committed_AS: 18446744073709454080 kB
> 6 Committed_AS: 18446744073709320960 kB
Because NR_CPUS can be greater than 1000 and meminfo_proc_show() does
not check for underflow.
But NR_CPUS proportional isn't good calculation. In general,
possibility of lock contention is proportional to the number of online
cpus, not theorical maximum cpus (NR_CPUS).
The current kernel has generic percpu-counter stuff. using it is right
way. it makes code simplify and percpu_counter_read_positive() don't
make underflow issue.
Reported-by: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Eric B Munson <ebmunson@us.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: <stable@kernel.org> [All kernel versions]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 30d1073..9872d6c 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -12,21 +12,18 @@
#ifdef __KERNEL__
#include <linux/mm.h>
+#include <linux/percpu_counter.h>
#include <asm/atomic.h>
extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
-extern atomic_long_t vm_committed_space;
+extern struct percpu_counter vm_committed_as;
-#ifdef CONFIG_SMP
-extern void vm_acct_memory(long pages);
-#else
static inline void vm_acct_memory(long pages)
{
- atomic_long_add(pages, &vm_committed_space);
+ percpu_counter_add(&vm_committed_as, pages);
}
-#endif
static inline void vm_unacct_memory(long pages)
{