linux-kernel - Re: mm: slab - __cache

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Message-ID: <28180.1227211108@turing-police.cc.vt.edu>
Date:	Thu, 20 Nov 2008 14:58:28 -0500
From:	Valdis.Kletnieks@...edu
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: mm: slab - __cache_alloc NULL prefetch fix

On Thu, 20 Nov 2008 19:44:00 +0300, Cyrill Gorcunov said:

> -	prefetchw(objp);
>  
> -	if (likely(objp))
> +	if (likely(objp)) {
> +		prefetchw(objp);
>  		kmemcheck_slab_alloc(cachep, flags, objp, obj_size(cachep));
> +	}

Although it probably makes sense to not bother prefetching NULL, I also
need to wonder how useful it is to prefetch something that we then
turn around and dereference in the very next line of code.

Maybe we should just lose the prefetch entirely?

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