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

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Date:	Thu, 25 Jan 2007 14:35:29 +0800
From:	"Aubrey Li" <aubreylee@...il.com>
To:	"Vaidyanathan Srinivasan" <svaidy@...ux.vnet.ibm.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

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.

-Aubrey
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