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

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Message-ID: <20070928205952.GA30404@skynet.ie>
Date:	Fri, 28 Sep 2007 21:59:52 +0100
From:	mel@...net.ie (Mel Gorman)
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Christoph Lameter <clameter@....com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@....de>, 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 (28/09/07 20:25), Peter Zijlstra didst pronounce:
> 
> 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

The 12MB is related to the size of pageblock_order. I strongly suspect
that if you forced pageblock_order to be something like 4 or 5, the
min_free_kbytes would not need to be raised. The current values are
selected based on the hugepage size.

> 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..
> 

-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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