From: David Rientjes <rientjes@google.com>
Subject: Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and
 kzalloc
Date: Wed, 25 Aug 2010 20:12:04 -0700 (PDT)
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Cc: Peter Zijlstra <peterz@infradead.org>,
	Dave Chinner <david@fromorbit.com>, "Ted Ts'o" <tytso@mit.edu>,
	Jens Axboe <jaxboe@fusionio.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Neil Brown <neilb@suse.de>, Alasdair G Kergon <agk@redhat.com>,
	Chris Mason <chris.mason@oracle.com>,
	Steven Whitehouse <swhiteho@redhat.com>,
	Jan Kara <jack@suse.cz>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
	"cluster-devel@redhat.com" <cluster-devel@redhat.com>,
	"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
	"reiserfs-devel@vger.kernel.org" <reiserfs-devel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
To: Christoph Lameter <cl@linux.com>
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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.