From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Joe Perches <joe@perches.com>
Cc: linux-kernel@vger.kernel.org,
Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH] SLUB: Fix __GFP_ZERO unlikely() annotation
Date: Wed, 25 Nov 2009 20:30:36 +0200 [thread overview]
Message-ID: <4B0D77CC.3020807@cs.helsinki.fi> (raw)
In-Reply-To: <1259173636.29779.41.camel@Joe-Laptop.home>
Joe Perches wrote:
> 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))
Because that has no effect on the generated code.
next prev parent reply other threads:[~2009-11-25 18:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-25 18:21 [PATCH] SLUB: Fix __GFP_ZERO unlikely() annotation Pekka Enberg
2009-11-25 18:27 ` Joe Perches
2009-11-25 18:30 ` Pekka Enberg [this message]
2009-11-25 20:15 ` Christoph Lameter
2009-11-25 20:19 ` Pekka Enberg
2009-11-26 20:27 ` Pekka Enberg
2009-11-27 19:26 ` Christoph Lameter
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