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

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Date:	Thu, 17 May 2012 13:23:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...e.cz>
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 May 2012 14:10:49 +0200
Michal Hocko <mhocko@...e.cz> wrote:

> > > 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%

I turned the above into this soundbite:

: 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.  Total runtime was
: approximately tripled by commit 64574746 and this patch restores the
: previous throughput levels.

Was that truthful?
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