linux-kernel - Re: [PATCH 9/9] slab: remove a useless lockdep annotation

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Message-ID: <20140217061201.GA3468@lge.com>
Date:	Mon, 17 Feb 2014 15:12:01 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] slab: remove a useless lockdep annotation

On Fri, Feb 14, 2014 at 12:49:57PM -0600, Christoph Lameter wrote:
> On Fri, 14 Feb 2014, Joonsoo Kim wrote:
> 
> > @@ -921,7 +784,7 @@ static int transfer_objects(struct array_cache *to,
> >  static inline struct alien_cache **alloc_alien_cache(int node,
> >  						int limit, gfp_t gfp)
> >  {
> > -	return (struct alien_cache **)BAD_ALIEN_MAGIC;
> > +	return NULL;
> >  }
> >
> 
> Why change the BAD_ALIEN_MAGIC?

Hello, Christoph.

BAD_ALIEN_MAGIC is only checked by slab_set_lock_classes(). We remove this
function in this patch, so returning BAD_ALIEN_MAGIC is useless.
And, in fact, BAD_ALIEN_MAGIC is already useless, because alloc_alien_cache()
can't be called on !CONFIG_NUMA. This function is called if use_alien_caches
is positive, but on !CONFIG_NUMA, use_alien_caches is always 0. So we don't
have any chance to meet this BAD_ALIEN_MAGIC in runtime.

Thanks.
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