Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | Re: meminfo Committed_AS underflows | Date | Wed, 15 Apr 2009 13:12:56 +0900 (JST) |
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fix stupid mistake.
Changelog: since v1 - change the type of commited value from ulong to long
========================= Subject: [PATCH v2] fix Commited_AS underflow
Dave Hansen reported committed_AS field can underfolow.
> # 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_CPU can be greater than 1000. and meminfo_proc_show() doesn't have underflow check.
this patch have two change.
1. Change NR_CPU to nr_online_cpus() vm_acct_memory() isn't fast-path. then cpumask_weight() calculation isn't so expensive and the parameter for scalability issue should consider number of _physical_ cpus. not theoretical maximum number. 2. Add under-flow check to meminfo_proc_show(). Almost field in /proc/meminfo have underflow check. but Committed_AS is significant exeption. it should do.
Reported-by: Dave Hansen <dave@linux.vnet.ibm.com> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> --- fs/proc/meminfo.c | 4 +++- mm/swap.c | 2 +- 2 files changed, 4 insertions(+), 2 deletions(-)
Index: b/fs/proc/meminfo.c =================================================================== --- a/fs/proc/meminfo.c +++ b/fs/proc/meminfo.c @@ -22,7 +22,7 @@ void __attribute__((weak)) arch_report_m static int meminfo_proc_show(struct seq_file *m, void *v) { struct sysinfo i; - unsigned long committed; + long committed; unsigned long allowed; struct vmalloc_info vmi; long cached; @@ -36,6 +36,8 @@ static int meminfo_proc_show(struct seq_ si_meminfo(&i); si_swapinfo(&i); committed = atomic_long_read(&vm_committed_space); + if (committed < 0) + committed = 0; allowed = ((totalram_pages - hugetlb_total_pages()) * sysctl_overcommit_ratio / 100) + total_swap_pages; Index: b/mm/swap.c =================================================================== --- a/mm/swap.c +++ b/mm/swap.c @@ -519,7 +519,7 @@ EXPORT_SYMBOL(pagevec_lookup_tag); * We tolerate a little inaccuracy to avoid ping-ponging the counter between * CPUs */ -#define ACCT_THRESHOLD max(16, NR_CPUS * 2) +#define ACCT_THRESHOLD max_t(long, 16, num_online_cpus() * 2) static DEFINE_PER_CPU(long, committed_space);
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