linux-kernel - Re: [PATCH] mm: do not drain pagevecs for mlock

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Message-ID: <CAHGf_=qOGy3MQgiFyfeG82+gbDXTBT5KQjgR7JqMfQ7e7RSGpA@mail.gmail.com>
Date:	Fri, 30 Dec 2011 03:11:49 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Tao Ma <tm@....ma>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <jweiner@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: do not drain pagevecs for mlock

2011/12/30 Tao Ma <tm@....ma>:
> In our test of mlock, we have found some severe performance regression
> in it. Some more investigations show that mlocked is blocked heavily
> by lur_add_drain_all which calls schedule_on_each_cpu and flush the work
> queue which is very slower if we have several cpus.
>
> So we have tried 2 ways to solve it:
> 1. Add a per cpu counter for all the pagevecs so that we don't schedule
>   and flush the lru_drain work if the cpu doesn't have any pagevecs(I
>   have finished the codes already).
> 2. Remove the lru_add_drain_all.
>
> The first one has some problems since in our product system, all the cpus
> are busy, so I guess there is very little chance for a cpu to have 0 pagevecs
> except that you run several consecutive mlocks.
>
> From the commit log which added this function(8891d6da), it seems that we
> don't have to call it. So the 2nd one seems to be both easy and workable and
> comes this patch.

Could you please show us your system environment and benchmark programs?
Usually lru_drain_** is very fast than mlock() body because it makes
plenty memset(page).
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