linux-kernel - Re: mapped pagecache pages vs unmapped pages

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Message-ID: <4F838390.1080909@redhat.com>
Date:	Mon, 09 Apr 2012 20:49:20 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Alexey Ivanov <rbtz@...dex-team.ru>,
	"gnehzuil.lzheng@...il.com" <gnehzuil.lzheng@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, yinghan@...gle.com
Subject: Re: mapped pagecache pages vs unmapped pages

On 04/09/2012 08:31 PM, Minchan Kim wrote:
> 2012-04-10 오전 8:50, Alexey Ivanov 쓴 글:
>
>> Did you consider making this ratio tunable, at least manually(i.e. via sysctl)?
>> I suppose we are not the only ones with almost-whole-ram-mmaped workload.
>
> Personally, I think it's not good approach.
> It depends on kernel's internal implemenatation which would be changed
> in future as we chagend it at 2.6.28.

I also believe that a tunable for this is not going to be
a very workable approach, for the simple reason that changing
the value does not make a predictable change in the effectiveness
of working set detection or protection.

> In my opinion, kernel just should do best effort to keep active working
> set except some critical pages which are code pages.

Johannes has some experimental code to measure refaults, and
calculate their distance in a multi-zone, multi-cgroup environment.

That would allow us to predictably place things in the working set
as required.

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