linux-kernel - Re: [PATCH -mm 1/2] memcg: get rid of memcg_create_cache

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Date:	Thu, 8 May 2014 11:08:54 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Michal Hocko <mhocko@...e.cz>, <hannes@...xchg.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH -mm 1/2] memcg: get rid of memcg_create_cache_name

On Wed, May 07, 2014 at 01:53:52PM -0700, Andrew Morton wrote:
> On Wed, 7 May 2014 14:45:16 +0400 Vladimir Davydov <vdavydov@...allels.com> wrote:
> 
> > @@ -3164,6 +3141,7 @@ void memcg_free_cache_params(struct kmem_cache *s)
> >  static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
> >  				    struct kmem_cache *root_cache)
> >  {
> > +	static char *memcg_name_buf;	/* protected by memcg_slab_mutex */
> >  	struct kmem_cache *cachep;
> >  	int id;
> >  
> > @@ -3179,7 +3157,14 @@ static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
> >  	if (cache_from_memcg_idx(root_cache, id))
> >  		return;
> >  
> > -	cachep = kmem_cache_create_memcg(memcg, root_cache);
> > +	if (!memcg_name_buf) {
> > +		memcg_name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
> > +		if (!memcg_name_buf)
> > +			return;
> > +	}
> 
> Does this have any meaningful advantage over the simpler
> 
> 	static char memcg_name_buf[NAME_MAX + 1];
> 
> ?

Don't think so. In case nobody has objections, the patch is attached
below.

Thanks.
--

From: Vladimir Davydov <vdavydov@...allels.com>
Subject: [PATCH] memcg: memcg_kmem_create_cache: make memcg_name_buf
 statically allocated

It isn't worth complicating the code by allocating it on the first
access, because it only takes 256 bytes.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9ff3742f4154..01fda17a2566 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3141,7 +3141,8 @@ void memcg_free_cache_params(struct kmem_cache *s)
 static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
 				    struct kmem_cache *root_cache)
 {
-	static char *memcg_name_buf;	/* protected by memcg_slab_mutex */
+	static char memcg_name_buf[NAME_MAX + 1]; /* protected by
+						     memcg_slab_mutex */
 	struct kmem_cache *cachep;
 	int id;
 
@@ -3157,12 +3158,6 @@ static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
 	if (cache_from_memcg_idx(root_cache, id))
 		return;
 
-	if (!memcg_name_buf) {
-		memcg_name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
-		if (!memcg_name_buf)
-			return;
-	}
-
 	cgroup_name(memcg->css.cgroup, memcg_name_buf, NAME_MAX + 1);
 	cachep = kmem_cache_create_memcg(memcg, root_cache, memcg_name_buf);
 	/*
--
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