linux-kernel - Re: [patch v2 1/5] mm: add nofail variants of kmalloc kcalloc and kzalloc

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Message-ID: <alpine.DEB.2.00.1009051602130.5003@chino.kir.corp.google.com>
Date:	Sun, 5 Sep 2010 16:03:52 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Neil Brown <neilb@...e.de>
cc:	Jan Kara <jack@...e.cz>, Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alasdair G Kergon <agk@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-raid@...r.kernel.org, linux-btrfs@...r.kernel.org,
	cluster-devel@...hat.com, linux-ext4@...r.kernel.org,
	reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v2 1/5] mm: add nofail variants of kmalloc kcalloc and
 kzalloc

On Fri, 3 Sep 2010, Neil Brown wrote:

> I'm actually a bit confused about this too.
> I thought David said he was removing a branch on the *slow* path - which make
> sense as you wouldn't even test NOFAIL until you had a failure.
> Why are branches on the slow-path an issue??

They aren't necessarily an issue in the performance sense, this is a 
cleanup series since all converted callers to using these new functions 
(and the eventual removal of __GFP_NOFAIL entirely) are using the bit 
unnecessarily since they all have orders that implicitly loop in the page 
allocator forever already, with or without the flag.
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