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From: Christoph Lameter <cl@linux.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: Vinayak Menon <vinmenon@codeaurora.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, hannes@cmpxchg.org,
	vdavydov@parallels.com, mgorman@suse.de, minchan@kernel.org
Subject: Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated
Date: Mon, 26 Jan 2015 12:35:00 -0600 (CST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1501261233550.16786@gentwo.org> (raw)
In-Reply-To: <20150126174606.GD22681@dhcp22.suse.cz>

On Mon, 26 Jan 2015, Michal Hocko wrote:

> > Please do not run the vmstat_updates concurrently. They update shared
> > cachelines and therefore can cause bouncing cachelines if run concurrently
> > on multiple cpus.
>
> Would you preffer to call smp_call_function_single on each CPU
> which needs an update? That would make vmstat_shepherd slower but that
> is not a big deal, is it?

Run it from the timer interrupt as usual from a work request? Those are
staggered.

> Anyway I am wondering whether the cache line bouncing between
> vmstat_update instances is a big deal in the real life. Updating shared
> counters whould bounce with many CPUs but this is an operation which is
> not done often. Also all the CPUs would have update the same counters
> all the time and I am not sure this happens that often. Do you have a
> load where this would be measurable?

Concurrent page faults update lots of counters concurrently. But will
those trigger the smp_call_function?

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Lameter <cl@linux.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: Vinayak Menon <vinmenon@codeaurora.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org, hannes@cmpxchg.org,
	vdavydov@parallels.com, mgorman@suse.de, minchan@kernel.org
Subject: Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated
Date: Mon, 26 Jan 2015 12:35:00 -0600 (CST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1501261233550.16786@gentwo.org> (raw)
In-Reply-To: <20150126174606.GD22681@dhcp22.suse.cz>

On Mon, 26 Jan 2015, Michal Hocko wrote:

> > Please do not run the vmstat_updates concurrently. They update shared
> > cachelines and therefore can cause bouncing cachelines if run concurrently
> > on multiple cpus.
>
> Would you preffer to call smp_call_function_single on each CPU
> which needs an update? That would make vmstat_shepherd slower but that
> is not a big deal, is it?

Run it from the timer interrupt as usual from a work request? Those are
staggered.

> Anyway I am wondering whether the cache line bouncing between
> vmstat_update instances is a big deal in the real life. Updating shared
> counters whould bounce with many CPUs but this is an operation which is
> not done often. Also all the CPUs would have update the same counters
> all the time and I am not sure this happens that often. Do you have a
> load where this would be measurable?

Concurrent page faults update lots of counters concurrently. But will
those trigger the smp_call_function?

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  reply	other threads:[~2015-01-26 18:35 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-14 11:36 [PATCH v2] mm: vmscan: fix the page state calculation in too_many_isolated Vinayak Menon
2015-01-14 11:36 ` Vinayak Menon
2015-01-14 16:50 ` Michal Hocko
2015-01-14 16:50   ` Michal Hocko
2015-01-15 17:24   ` Vinayak Menon
2015-01-15 17:24     ` Vinayak Menon
2015-01-16 15:49     ` Michal Hocko
2015-01-16 15:49       ` Michal Hocko
2015-01-16 17:57       ` Michal Hocko
2015-01-16 17:57         ` Michal Hocko
2015-01-16 19:17         ` Christoph Lameter
2015-01-16 19:17           ` Christoph Lameter
2015-01-17 15:18       ` Vinayak Menon
2015-01-17 15:18         ` Vinayak Menon
2015-01-17 19:48         ` Christoph Lameter
2015-01-17 19:48           ` Christoph Lameter
2015-01-19  4:27           ` Vinayak Menon
2015-01-19  4:27             ` Vinayak Menon
2015-01-21 14:39             ` Michal Hocko
2015-01-21 14:39               ` Michal Hocko
2015-01-22 15:16               ` Vlastimil Babka
2015-01-22 15:16                 ` Vlastimil Babka
2015-01-22 16:11               ` Christoph Lameter
2015-01-22 16:11                 ` Christoph Lameter
2015-01-26 17:46                 ` Michal Hocko
2015-01-26 17:46                   ` Michal Hocko
2015-01-26 18:35                   ` Christoph Lameter [this message]
2015-01-26 18:35                     ` Christoph Lameter
2015-01-27 10:52                     ` Michal Hocko
2015-01-27 10:52                       ` Michal Hocko
2015-01-27 16:59                       ` Christoph Lameter
2015-01-27 16:59                         ` Christoph Lameter
2015-01-30 15:28                         ` Michal Hocko
2015-01-30 15:28                           ` Michal Hocko
2015-01-26 17:28           ` Michal Hocko
2015-01-26 17:28             ` Michal Hocko
2015-01-26 18:35             ` Christoph Lameter
2015-01-26 18:35               ` Christoph Lameter
2015-01-26 22:11             ` Andrew Morton
2015-01-26 22:11               ` Andrew Morton
2015-01-27 10:41               ` Michal Hocko
2015-01-27 10:41                 ` Michal Hocko
2015-01-27 10:33             ` Vinayak Menon
2015-01-27 10:33               ` Vinayak Menon
2015-01-27 10:45               ` Michal Hocko
2015-01-27 10:45                 ` Michal Hocko
2015-01-29 17:32       ` Christoph Lameter
2015-01-29 17:32         ` Christoph Lameter
2015-01-30 15:27         ` Michal Hocko
2015-01-30 15:27           ` Michal Hocko
2015-01-16  1:17 ` Andrew Morton
2015-01-16  1:17   ` Andrew Morton
2015-01-16  5:10   ` Vinayak Menon
2015-01-16  5:10     ` Vinayak Menon
2015-01-17 16:29   ` Vinayak Menon
2015-01-17 16:29     ` Vinayak Menon
2015-02-11 22:14     ` Andrew Morton
2015-02-11 22:14       ` Andrew Morton
2015-02-12 16:19       ` Vlastimil Babka
2015-02-12 16:19         ` Vlastimil Babka

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