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

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Message-ID: <alpine.DEB.2.00.1008252010260.10986@chino.kir.corp.google.com>
Date:	Wed, 25 Aug 2010 20:12:04 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Dave Chinner <david@...morbit.com>, "Ted Ts'o" <tytso@....edu>,
	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, 25 Aug 2010, Christoph Lameter wrote:

> > Right, I thought you said the slab layer passes __GFP_NOFAIL when there's
> > no objects available.
> 
> Yes, the slab layer calls the page allocator when there are no objects
> available and passes the __GFP_NOFAIL that the user may have set in the
> call to the page allocator.
> 
> Why then add new functions that do the same?
> 

Because we can remove the flag, remove branches from the page allocator 
slowpath, and none of these allocations actually are dependent on 
__GFP_NOFAIL since they are all under PAGE_ALLOC_COSTLY_ORDER.
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