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Date: Tue, 28 Apr 2009 12:07:59 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: kosaki.motohiro@...fujitsu.com, balbir@...ux.vnet.ibm.com,
dave@...ux.vnet.ibm.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, ebmunson@...ibm.com,
mel@...ux.vnet.ibm.com, cl@...ux-foundation.org
Subject: Re: meminfo Committed_AS underflows
> On Wed, 15 Apr 2009 14:17:13 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>
> > * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-04-15 13:10:06]:
> >
> > > > * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-04-15 11:04:59]:
> > > >
> > > > > committed = atomic_long_read(&vm_committed_space);
> > > > > + if (committed < 0)
> > > > > + committed = 0;
> > > >
>
> Is there a reason why we can't use a boring old percpu_counter for
> vm_committed_space? That way the meminfo code can just use
> percpu_counter_read_positive().
>
> Or perhaps just percpu_counter_read(). The percpu_counter code does a
> better job of handling large cpu counts than the
> mysteriously-duplicative open-coded stuff we have there.
At that time, I thought smallest patch is better because it can send -stable
tree easily.
but maybe I was wrong. it made bikeshed discussion :(
ok, I'm going to right way.
=========================================
Subject: [PATCH] fix Committed_AS underfolow on large NR_CPUS environment
As reported by Dave Hansen, 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@...ux.vnet.ibm.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Eric B Munson <ebmunson@...ibm.com>
---
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(-)
Index: b/fs/proc/meminfo.c
===================================================================
--- a/fs/proc/meminfo.c 2009-04-28 11:36:43.000000000 +0900
+++ b/fs/proc/meminfo.c 2009-04-28 11:36:54.000000000 +0900
@@ -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;
Index: b/mm/mmap.c
===================================================================
--- a/mm/mmap.c 2009-04-28 11:36:43.000000000 +0900
+++ b/mm/mmap.c 2009-04-28 11:36:54.000000000 +0900
@@ -85,7 +85,7 @@ 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
@@ -179,11 +179,7 @@ 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);
@@ -2481,4 +2477,8 @@ 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);
}
Index: b/mm/nommu.c
===================================================================
--- a/mm/nommu.c 2009-04-28 11:36:43.000000000 +0900
+++ b/mm/nommu.c 2009-04-28 11:36:54.000000000 +0900
@@ -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(vm_region, SLAB_PANIC);
}
@@ -1847,12 +1851,9 @@ 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);
Index: b/mm/swap.c
===================================================================
--- a/mm/swap.c 2009-04-28 11:36:43.000000000 +0900
+++ b/mm/swap.c 2009-04-28 11:36:54.000000000 +0900
@@ -491,49 +491,6 @@ 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
*/
@@ -554,7 +511,4 @@ 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
}
Index: b/include/linux/mman.h
===================================================================
--- a/include/linux/mman.h 2009-04-28 11:32:47.000000000 +0900
+++ b/include/linux/mman.h 2009-04-28 11:38:42.000000000 +0900
@@ -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)
{
--
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