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Subject[patch 54/58] mm: fix Committed_AS underflow on large NR_CPUS environment
2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

commit 00a62ce91e554198ef28234c91c36f850f5a3bc9 upstream

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/proc/meminfo.c | 2 +-
include/linux/mman.h | 9 +++------
mm/mmap.c | 12 ++++++------
mm/nommu.c | 13 +++++++------
mm/swap.c | 46 ----------------------------------------------
5 files changed, 17 insertions(+), 65 deletions(-)
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -35,7 +35,7 @@ static int meminfo_proc_show(struct seq_
#define K(x) ((x) << (PAGE_SHIFT - 10))
si_meminfo(&i);
si_swapinfo(&i);
- committed = atomic_long_read(&vm_committed_space);
+ committed = percpu_counter_read_positive(&vm_committed_as);
allowed = ((totalram_pages - hugetlb_total_pages())
* sysctl_overcommit_ratio / 100) + total_swap_pages;

--- 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)
{
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -84,7 +84,7 @@ EXPORT_SYMBOL(vm_get_page_prot);
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
-atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
+struct percpu_counter vm_committed_as;

/*
* Check that a process has enough memory to allocate a new virtual
@@ -178,11 +178,7 @@ int __vm_enough_memory(struct mm_struct
if (mm)
allowed -= mm->total_vm / 32;

- /*
- * cast `allowed' as a signed long because vm_committed_space
- * sometimes has a negative value
- */
- if (atomic_long_read(&vm_committed_space) < (long)allowed)
+ if (percpu_counter_read_positive(&vm_committed_as) < allowed)
return 0;
error:
vm_unacct_memory(pages);
@@ -2477,6 +2473,10 @@ void mm_drop_all_locks(struct mm_struct
*/
void __init mmap_init(void)
{
+ int ret;
+
+ ret = percpu_counter_init(&vm_committed_as, 0);
+ VM_BUG_ON(ret);
vm_area_cachep = kmem_cache_create("vm_area_struct",
sizeof(struct vm_area_struct), 0,
SLAB_PANIC, NULL);
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -62,7 +62,7 @@ void *high_memory;
struct page *mem_map;
unsigned long max_mapnr;
unsigned long num_physpages;
-atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
+struct percpu_counter vm_committed_as;
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
@@ -463,6 +463,10 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
*/
void __init mmap_init(void)
{
+ int ret;
+
+ ret = percpu_counter_init(&vm_committed_as, 0);
+ VM_BUG_ON(ret);
vm_region_jar = kmem_cache_create("vm_region_jar",
sizeof(struct vm_region), 0,
SLAB_PANIC, NULL);
@@ -1849,12 +1853,9 @@ int __vm_enough_memory(struct mm_struct
if (mm)
allowed -= mm->total_vm / 32;

- /*
- * cast `allowed' as a signed long because vm_committed_space
- * sometimes has a negative value
- */
- if (atomic_long_read(&vm_committed_space) < (long)allowed)
+ if (percpu_counter_read_positive(&vm_committed_as) < allowed)
return 0;
+
error:
vm_unacct_memory(pages);

--- a/mm/swap.c
+++ b/mm/swap.c
@@ -514,49 +514,6 @@ unsigned pagevec_lookup_tag(struct pagev

EXPORT_SYMBOL(pagevec_lookup_tag);

-#ifdef CONFIG_SMP
-/*
- * We tolerate a little inaccuracy to avoid ping-ponging the counter between
- * CPUs
- */
-#define ACCT_THRESHOLD max(16, NR_CPUS * 2)
-
-static DEFINE_PER_CPU(long, committed_space);
-
-void vm_acct_memory(long pages)
-{
- long *local;
-
- preempt_disable();
- local = &__get_cpu_var(committed_space);
- *local += pages;
- if (*local > ACCT_THRESHOLD || *local < -ACCT_THRESHOLD) {
- atomic_long_add(*local, &vm_committed_space);
- *local = 0;
- }
- preempt_enable();
-}
-
-#ifdef CONFIG_HOTPLUG_CPU
-
-/* Drop the CPU's cached committed space back into the central pool. */
-static int cpu_swap_callback(struct notifier_block *nfb,
- unsigned long action,
- void *hcpu)
-{
- long *committed;
-
- committed = &per_cpu(committed_space, (long)hcpu);
- if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
- atomic_long_add(*committed, &vm_committed_space);
- *committed = 0;
- drain_cpu_pagevecs((long)hcpu);
- }
- return NOTIFY_OK;
-}
-#endif /* CONFIG_HOTPLUG_CPU */
-#endif /* CONFIG_SMP */
-
/*
* Perform any setup for the swap system
*/
@@ -577,7 +534,4 @@ void __init swap_setup(void)
* Right now other parts of the system means that we
* _really_ don't want to cluster much more
*/
-#ifdef CONFIG_HOTPLUG_CPU
- hotcpu_notifier(cpu_swap_callback, 0);
-#endif
}



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