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

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Date:	Wed, 25 Aug 2010 16:13:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ted Ts'o <tytso@....edu>
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, 2010-08-25 at 07:24 -0400, Ted Ts'o wrote:
> There are other places where we can fail safely (for example, in jbd's
> start_this_handle, although that just pushes the layer up the stack,
> and ultimately, to userspace where most userspace programs don't
> really expect ENOMEM to get returned by a random disk write 

While talking with Chris about this, if you can indeed push the error
out that far you can basically ensure this particular fs-op does not
complicate the journal commit and thereby limit the number of extra
entries in your journal, and thus the amount of memory required.

So once stuff starts failing, push out ops back out of the filesystem
code, force a journal commit, and then let these ops retry. There is no
need to actually push the -ENOMEM all the way back to userspace.


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