linux-kernel - Re: [15/17] SLUB: Support virtual fallback via SLAB

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Date:	Fri, 28 Sep 2007 20:25:50 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [15/17] SLUB: Support virtual fallback via SLAB_VFALLBACK


On Fri, 2007-09-28 at 11:20 -0700, Christoph Lameter wrote:

> > start 2 processes that each mmap a separate 64M file, and which does
> > sequential writes on them. start a 3th process that does the same with
> > 64M anonymous.
> > 
> > wait for a while, and you'll see order=1 failures.
> 
> Really? That means we can no longer even allocate stacks for forking.
> 
> Its surprising that neither lumpy reclaim nor the mobility patches can 
> deal with it? Lumpy reclaim should be able to free neighboring pages to 
> avoid the order 1 failure unless there are lots of pinned pages.
> 
> I guess then that lots of pages are pinned through I/O?

memory got massively fragemented, as anti-frag gets easily defeated.
setting min_free_kbytes to 12M does seem to solve it - it forces 2 max
order blocks to stay available, so we don't mix types. however 12M on
128M is rather a lot.

its still on my todo list to look at it further..

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