linux-kernel - Re: [PATCH] mm: consider all swapped back pages in used-once logic

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Date:	Thu, 17 May 2012 14:10:49 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mel@....ul.ie>, Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm: consider all swapped back pages in used-once logic

On Thu 17-05-12 02:24:12, Andrew Morton wrote:
> On Thu, 17 May 2012 11:13:53 +0200 Michal Hocko <mhocko@...e.cz> wrote:
> 
> > [64574746 vmscan: detect mapped file pages used only once] made mapped pages
> > have another round in inactive list because they might be just short
> > lived and so we could consider them again next time. This heuristic
> > helps to reduce pressure on the active list with a streaming IO
> > worklods.
> > This patch fixes a regression introduced by this commit for heavy shmem
> 
> A performance regression, specifically.
> 
> Are you able to quantify it?

The customer's workload is shmem backed database (80% of RAM) and
they are measuring transactions/s with an IO in the background (20%).
Transactions touch more or less random rows in the table.
The rate goes down drastically when we start swapping out memory.

Numbers are more descriptive (without the patch is 100%, with 5
representative runs)
Average rate	315.83%
Best rate	131.76%
Worst rate	641.25%

Standard deviation (calibrated to average) is ~4% while without the
patch we are at 62.82%. 
The big variance without the patch is caused by the excessive swapping
which doesn't occur with the patch applied.

* Worst run (100%) compared to a random run with the patch
pgpgin	pswpin	pswpout	pgmajfault
1.58%	0.00%	0.01%	0.22%

Average size of the LRU lists:
nr_inactive_anon nr_active_anon nr_inactive_file nr_active_file
52.91%           7234.72%       249.39%          126.64%

* Best run
pgpgin	pswpin	pswpout	pgmajfault
3.37%	0.00%	0.11%	0.39%

nr_inactive_anon nr_active_anon nr_inactive_file nr_active_file
49.85%           3868.74%       175.03%          121.27%

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
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