linux-kernel - Re: [PATCH 0/5] make slab gfp fair

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Message-ID: <Pine.LNX.4.64.0705171101360.18085@schroedinger.engr.sgi.com>
Date:	Thu, 17 May 2007 11:02:51 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Matt Mackall <mpm@...enic.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thomas Graf <tgraf@...g.ch>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/5] make slab gfp fair

On Thu, 17 May 2007, Matt Mackall wrote:

> Simply stated, the problem is sometimes it's impossible to free memory
> without allocating more memory. Thus we must keep enough protected
> reserve that we can guarantee progress. This is what mempools are for
> in the regular I/O stack. Unfortunately, mempools are a bad match for
> network I/O.
> 
> It's absolutely correct that performance doesn't matter in the case
> this patch is addressing. All that matters is digging ourselves out of
> OOM. The box either survives the crisis or it doesn't.

Well we fail allocations in order to do so and these allocations may be 
even nonatomic allocs. Pretty dangerous approach.

> It's also correct that we should hardly ever get into a situation
> where we trigger this problem. But such cases are still fairly easy to
> trigger in some workloads. Swap over network is an excellent example,
> because we typically don't start swapping heavily until we're quite
> low on freeable memory.

Is it not possible to avoid failing allocs? Instead put processes to 
sleep? Run synchrononous reclaim?

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