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Message-ID: <47FA94AE.4070803@cs.helsinki.fi>
Date: Tue, 08 Apr 2008 00:39:58 +0300
From: Pekka Enberg <penberg@cs.helsinki.fi>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Hugh Dickins <hugh@veritas.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Christoph Lameter <clameter@sgi.com>,
       James Bottomley <James.Bottomley@HansenPartnership.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
       Jens Axboe <jens.axboe@oracle.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] scsi: fix sense_slab/bio swapping livelock
References: <Pine.LNX.4.64.0804062348001.19446@blonde.site>  <Pine.LNX.4.64.0804062213230.18148@schroedinger.engr.sgi.com>  <Pine.LNX.4.64.0804072000410.18591@blonde.site> <1207598115.29991.23.camel@lappy> <Pine.LNX.4.64.0804072121320.28744@blonde.site> <47FA8B5A.5090104@cs.helsinki.fi> <47FA8CB0.6070106@cs.helsinki.fi> <alpine.LFD.1.00.0804071409150.2886@woody.linux-foundation.org> <47FA937E.6000009@cs.helsinki.fi>
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Linus Torvalds wrote:
>> I suspect the right thing to do is not to mark them for "IO", but mark 
>> them for "short-lived", and allow short-lived allocations that don't 
>> have extended lifetimes to succeed even when a "real" allocation 
>> wouldn't.

Pekka Enberg wrote:
> Yeah, makes sense. We do have GFP_TEMPORARY so we could associate this 
> new semantics with that. But the real problem here is how to do the 
> "allocate harder" part which, btw, sounds very similar to what Peter's 
> kmalloc reserve patches try to do...

Actually, a trivial way to implement that is to have a few "emergency 
kmalloc" caches say for sizes 64, 128, 256, and 512 that have some 
pre-allocated pages into which these GFP_TEMPORARY allocations are 
allowed to dip into on OOM and OOM only.

		Pekka