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

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Message-ID: <Pine.LNX.4.64.0709281133570.5397@schroedinger.engr.sgi.com>
Date:	Fri, 28 Sep 2007 11:41:18 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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, 28 Sep 2007, Peter Zijlstra wrote:

> 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.

Yes, strict ordering would be much better. On NUMA it may be possible to 
completely forbid merging. We can fall back to other nodes if necessary. 
12M is not much on a NUMA system.

But this shows that (unsurprisingly) we may have issues on systems with a 
small amounts of memory and we may not want to use higher orders on such 
systems.

The case you got may be good to use as a testcase for the virtual 
fallback. Hmmmm... Maybe it is possible to allocate the stack as a virtual 
compound page. Got some script/code to produce that problem?
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