linux-kernel - Re: [PATCH] SLUB: Fix __GFP

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Date:	Wed, 25 Nov 2009 10:27:16 -0800
From:	Joe Perches <joe@...ches.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	linux-kernel@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] SLUB: Fix __GFP_ZERO unlikely() annotation

On Wed, 2009-11-25 at 20:21 +0200, Pekka Enberg wrote:
> The unlikely() annotation in slab_alloc() covers too much of the expression.
> It's actually very likely that the object is not NULL so use unlikely() only
> for the __GFP_ZERO expression like SLAB does.
[]
> +++ b/mm/slub.c
> @@ -1735,7 +1735,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
> -	if (unlikely((gfpflags & __GFP_ZERO) && object))
> +	if (unlikely(gfpflags & __GFP_ZERO) && object)
>  		memset(object, 0, objsize);

so why not use

	if (unlikely(gfpflags & __GFP_ZERO) && likely(object))


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