linux-kernel - Re: [PATCH v3 2/9] slab: move up code to get kmem_cache_node in free

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Message-ID: <20140702003952.GA9972@js1304-P5Q-DELUXE>
Date:	Wed, 2 Jul 2014 09:39:52 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Vladimir Davydov <vdavydov@...allels.com>
Subject: Re: [PATCH v3 2/9] slab: move up code to get kmem_cache_node in
 free_block()

On Tue, Jul 01, 2014 at 03:21:21PM -0700, David Rientjes wrote:
> On Tue, 1 Jul 2014, Joonsoo Kim wrote:
> 
> > node isn't changed, so we don't need to retreive this structure
> > everytime we move the object. Maybe compiler do this optimization,
> > but making it explicitly is better.
> > 
> 
> Qualifying the pointer as const would be even more explicit.

Hello,

So what you recommend is something likes below?

-       struct kmem_cache_node *n = get_node(cachep, node);
+       struct kmem_cache_node * const n = get_node(cachep, node);

I don't have seen this form of code protecting pointer itself in mm.
Instead, I have seen 'const struct kmem_cache_node *n' which protects
memory pointed by pointer. But this case isn't that case.

Am I missing something?

> 
> > Acked-by: Christoph Lameter <cl@...ux.com>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> Acked-by: David Rientjes <rientjes@...gle.com>

Thank you!

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