linux-kernel - Re: [RFC] Limit the size of the pagecache

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Date:	Thu, 25 Jan 2007 13:19:52 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Aubrey Li <aubreylee@...il.com>
CC:	Christoph Lameter <clameter@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Robin Getz <rgetz@...ckfin.uclinux.org>,
	"Hennerich, Michael" <Michael.Hennerich@...log.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] Limit the size of the pagecache



Aubrey Li wrote:
> On 1/25/07, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
>>
>> Christoph Lameter wrote:
>>> On Wed, 24 Jan 2007, Vaidyanathan Srinivasan wrote:
>>>
>>>> With your patch, MMAP of a file that will cross the pagecache limit hangs the
>>>> system.  As I mentioned in my previous mail, without subtracting the
>>>> NR_FILE_MAPPED, the reclaim will infinitely try and fail.
>>> Well mapped pages are still pagecache pages.
>>>
>> Yes, but they can be classified under a process RSS pages.  Whether it
>> is an anon page or shared mem or mmap of pagecache, it would show up
>> under RSS.  Those pages can be limited by RSS limiter similar to the
>> one we are discussing in pagecache limiter.  In my opinion, once a
>> file page is mapped by the process, then it should be treated at par
>> with anon pages.  Application programs generally do not mmap a file
>> page if the reuse for the content is very low.
>>
> 
> I agree, we shouldn't take mmapped page into account.
> But Vaidy - even with your patch, we are still using the existing
> reclaimer, that means we dont ensure that only page cache is
> reclaimed/limited. mapped pages will be hit also.
> I think we still need to add a new scancontrol field to lock mmaped
> pages and remove unmapped pagecache pages only.

I have tried to add scan control to Roy's patch at
http://lkml.org/lkml/2007/01/17/96

In that patch, we search and remove only pages that are not mapped.
We also remove referenced and hot pagecache pages which the normal
reclaimer is not expected to consider.

I will try to fit that logic in Christoph's patch and test.

--Vaidy

> -Aubrey
> -
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