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

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Date:	Sat, 29 Sep 2007 01:13:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Christoph Lameter <clameter@....com>,
	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, 28 Sep 2007 20:25:50 +0200 Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> 
> 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..
> 

That would be really really bad (as in: patch-dropping time) if those
order-1 allocations are not atomic.

What's the callsite? 
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