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SubjectRe: [PATCH v4 2/4] mm/util.c: make vm_memory_committed() more accurate
On Fri 29-05-20 09:06:08, Feng Tang wrote:
> percpu_counter_sum_positive() will provide more accurate info.
>
> As with percpu_counter_read_positive(), in worst case the deviation
> could be 'batch * nr_cpus', which is totalram_pages/256 for now,
> and will be more when the batch gets enlarged.
>
> Its time cost is about 800 nanoseconds on a 2C/4T platform and
> 2~3 microseconds on a 2S/36C/72T server in normal case, and in
> worst case where vm_committed_as's spinlock is under severe
> contention, it costs 30~40 microseconds for the 2S/36C/72T sever,
> which should be fine for its only two users: /proc/meminfo and
> HyperV balloon driver's status trace per second.
>
> Signed-off-by: Feng Tang <feng.tang@intel.com>

I cannot speak for HyperV part. Cc maintainers but this shouldn't be a
problem for meminfo.

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/util.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index 9b3be03..3c7a08c 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -790,7 +790,7 @@ struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
> */
> unsigned long vm_memory_committed(void)
> {
> - return percpu_counter_read_positive(&vm_committed_as);
> + return percpu_counter_sum_positive(&vm_committed_as);
> }
> EXPORT_SYMBOL_GPL(vm_memory_committed);
>
> --
> 2.7.4
>

--
Michal Hocko
SUSE Labs

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