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From: Michal Hocko <mhocko@kernel.org>
To: Feng Tang <feng.tang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>, Kees Cook <keescook@chromium.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Iurii Zaikin <yzaikin@google.com>,
	andi.kleen@intel.com, tim.c.chen@intel.com,
	dave.hansen@intel.com, ying.huang@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mm/util.c: make vm_memory_committed() more accurate
Date: Fri, 15 May 2020 09:23:07 +0200	[thread overview]
Message-ID: <20200515072307.GG29153@dhcp22.suse.cz> (raw)
In-Reply-To: <1588922717-63697-3-git-send-email-feng.tang@intel.com>

On Fri 08-05-20 15:25:16, Feng Tang wrote:
> percpu_counter_sum_positive() will provide more accurate info.

Why do we need that?

> 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 two users: /proc/meminfo and HV ballon
> driver's status trace per second.

OK, this explains that the additional overhead is not terrible but there
is no actual information on why the imprecision is a problem.

> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
>  mm/util.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 988d11e..3de78e9 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -774,7 +774,7 @@ 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

  reply	other threads:[~2020-05-15  7:23 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-08  7:25 [PATCH 0/3] make vm_committed_as_batch aware of vm overcommit policy Feng Tang
2020-05-08  7:25 ` [PATCH 1/3] proc/meminfo: avoid open coded reading of vm_committed_as Feng Tang
2020-05-15  7:22   ` Michal Hocko
2020-05-08  7:25 ` [PATCH 2/3] mm/util.c: make vm_memory_committed() more accurate Feng Tang
2020-05-15  7:23   ` Michal Hocko [this message]
2020-05-15  8:11     ` Feng Tang
2020-05-15  9:04       ` Michal Hocko
2020-05-15 13:01         ` Feng Tang
2020-05-08  7:25 ` [PATCH 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy Feng Tang
2020-05-08 11:24   ` Matthew Wilcox
2020-05-08 12:33     ` Feng Tang
2020-05-15  7:41   ` Michal Hocko
2020-05-15  8:02     ` Feng Tang
2020-05-15  9:08       ` Michal Hocko
2020-05-15 11:26         ` Feng Tang
2020-05-15  7:44   ` Michal Hocko
2020-05-15  8:38     ` Feng Tang
2020-05-21 21:27 ` [PATCH 0/3] make vm_committed_as_batch aware of " Qian Cai
2020-05-26 18:14   ` Qian Cai
2020-05-27  1:14     ` Andi Kleen
2020-05-27  1:43       ` Feng Tang
2020-05-27  1:46     ` Feng Tang
2020-05-27  2:25       ` Qian Cai
2020-05-27 10:46         ` Feng Tang
2020-05-27 12:05           ` Qian Cai
2020-05-27 13:33             ` Feng Tang
2020-05-27 15:42               ` Qian Cai
2020-05-28 14:18           ` Qian Cai
2020-05-28 15:10             ` Feng Tang
2020-05-28 15:21               ` Kleen, Andi
2020-05-29 15:43                 ` Feng Tang
2020-05-29 15:50                   ` Andi Kleen
2020-05-29 16:04                     ` Feng Tang
2020-05-28 15:48               ` Michal Hocko

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