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Subject: Re: Should we be using unlikely() around tests of GFP_ZERO?
From: Matt Mackall <mpm@selenic.com>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Christoph Lameter <cl@linux-foundation.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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Date: Mon, 03 Jan 2011 11:23:46 -0600
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On Sun, 2011-01-02 at 18:48 -0500, Theodore Ts'o wrote:
> Given the patches being busily submitted by trivial patch submitters to
> make use kmem_cache_zalloc(), et. al, I believe we should remove the
> unlikely() tests around the (gfp_flags & __GFP_ZERO) tests, such as:
> 
> -	if (unlikely((flags & __GFP_ZERO) && objp))
> +	if ((flags & __GFP_ZERO) && objp)
> 		memset(objp, 0, obj_size(cachep));
> 
> Agreed?  If so, I'll send a patch...

Sounds good to me.

We might consider dropping this flag and making the decision statically
(ie alloc vs zalloc), at least for slab objects.

-- 
Mathematics is the supreme nostalgia of our time.