linux-ext4 - Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and kzalloc

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Message-ID: <20100825115709.GD4453@thunk.org>
Date:	Wed, 25 Aug 2010 07:57:09 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>, Alasdair G Kergon <agk@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Jan Kara <jack@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
	"cluster-devel@...hat.com" <cluster-devel@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"reiserfs-devel@...r.kernel.org" <reiserfs-devel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and
 kzalloc

On Wed, Aug 25, 2010 at 01:35:32PM +0200, Peter Zijlstra wrote:
> On Wed, 2010-08-25 at 07:24 -0400, Ted Ts'o wrote:
> > Part of the problem is that we have a few places in the kernel where
> > failure is really not an option --- or rather, if we're going to fail
> > while we're in the middle of doing a commit, our choices really are
> > (a) retry the loop in the jbd layer (which Andrew really doesn't
> > like), (b) keep our own private cache of free memory so we don't fail
> > and/or loop, (c) fail the file system and mark it read-only, or (d)
> > panic. 
> 
> d) do the allocation before you're committed to going fwd and can still
> fail and back out.

Sure in some cases that can be done, but the commit has to happen at
some point, or we run out of journal space, at which point we're back
to (c) or (d).

						- Ted


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