linux-kernel - Re: The VFS cache is not freed when there is not enough free memory to allocate

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Message-Id: <1164192171.5968.186.camel@twins>
Date:	Wed, 22 Nov 2006 11:42:51 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Aubrey <aubreylee@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	mel <mel@....ul.ie>, Andy Whitcroft <apw@...dowen.org>
Subject: Re: The VFS cache is not freed when there is not enough free
	memory to allocate

On Wed, 2006-11-22 at 18:02 +0800, Aubrey wrote:
> On 11/22/06, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > Please see the
> > threads on Mel Gorman's Anti-Fragmentation and Linear/Lumpy reclaim in
> > the linux-mm archives.
> >
> 
> Thanks to point this. Is it already included in Linus' git tree?

No it is not.

> Well, the test application just use an exaggerated way to replicate the issue.
> 
> Actually, In the real work, the application such as mplayer, asterisk,
> etc will run into
> the above problem when run them at the second time. I think I have no
> reason to modify those kind of applications.

It comes from the choice of architecture, I'd not run general purpose
code like that on MMU-less hardware. But yeah, I see your point.

> My patch let kernel drop VFS cache in the low memory situation when
> the application requests more memory allocation, I don't think it's
> luck. You know, the application just wants to allocate 8
> 1Mbyte-blocks(order =9) and releasing VFS cache we can get almost
> 50Mbyte free memory.

Yes it does that, but there is no guarantee that those 50MB have a
single 1M contiguous region amongst them.

> The patch indeedly enabled many failed test cases on our side. But
> yes, I don't think it's the final solution. I'll try Mel's patch and
> update the results.

Mel's patches alone aren't quite enough, you also need some reclaim
modifications, I'll ping Andy to see how far he's on that.

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