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

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Message-ID: <4F069120.8060300@tao.ma>
Date:	Fri, 06 Jan 2012 14:13:52 +0800
From:	Tao Ma <tm@....ma>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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

Hi Kosaki,
On 12/30/2011 06:07 PM, KOSAKI Motohiro wrote:
>>> Because your test program is too artificial. 20sec/100000times =
>>> 200usec. And your
>>> program repeat mlock and munlock the exact same address. so, yes, if
>>> lru_add_drain_all() is removed, it become near no-op. but it's
>>> worthless comparision.
>>> none of any practical program does such strange mlock usage.
>> yes, I should say it is artificial. But mlock did cause the problem in
>> our product system and perf shows that the mlock uses the system time
>> much more than others. That's the reason we created this program to test
>> whether mlock really sucks. And we compared the result with
>> rhel5(2.6.18) which runs much much faster.
>>
>> And from the commit log you described, we can remove lru_add_drain_all
>> safely here, so why add it? At least removing it makes mlock much faster
>> compared to the vanilla kernel.
> 
> If we remove it, we lose to a test way of mlock. "Memlocked" field of
> /proc/meminfo
> show inaccurate number very easily. So, if 200usec is no avoidable,
> I'll ack you.
> But I'm not convinced yet.
Do you find something new for this?

Thanks
Tao
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