linux-kernel - [PATCH 01/23] slub: don't create a copy of the name string in kmem_cache

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Date:	Fri, 20 Apr 2012 18:57:09 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	<cgroups@...r.kernel.org>
Cc:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<devel@...nvz.org>, <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: [PATCH 01/23] slub: don't create a copy of the name string in kmem_cache_create

When creating a cache, slub keeps a copy of the cache name through
strdup. The slab however, doesn't do that. This means that everyone
registering caches have to keep a copy themselves anyway, since code
needs to work on all allocators.

Having slab create a copy of it as well may very well be the right
thing to do: but at this point, the callers are already there

My motivation for it comes from the kmem slab cache controller for
memcg. Because we create duplicate caches, having a more consistent
behavior here really helps.

I am sending the patch, however, more to probe on your opinion about
it. If you guys agree, but don't want to merge it - since it is not
fixing anything, nor improving any situation etc, I am more than happy
to carry it in my series until it gets merged (fingers crossed).

Signed-off-by: Glauber Costa <glommer@...allels.com>
CC: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
---
 mm/slub.c |   14 ++------------
 1 files changed, 2 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index ffe13fd..af8cee9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3925,7 +3925,6 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 		size_t align, unsigned long flags, void (*ctor)(void *))
 {
 	struct kmem_cache *s;
-	char *n;
 
 	if (WARN_ON(!name))
 		return NULL;
@@ -3949,26 +3948,20 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 		return s;
 	}
 
-	n = kstrdup(name, GFP_KERNEL);
-	if (!n)
-		goto err;
-
 	s = kmalloc(kmem_size, GFP_KERNEL);
 	if (s) {
-		if (kmem_cache_open(s, n,
+		if (kmem_cache_open(s, name,
 				size, align, flags, ctor)) {
 			list_add(&s->list, &slab_caches);
 			up_write(&slub_lock);
 			if (sysfs_slab_add(s)) {
 				down_write(&slub_lock);
 				list_del(&s->list);
-				kfree(n);
 				kfree(s);
 				goto err;
 			}
 			return s;
 		}
-		kfree(n);
 		kfree(s);
 	}
 err:
@@ -5212,7 +5205,6 @@ static void kmem_cache_release(struct kobject *kobj)
 {
 	struct kmem_cache *s = to_slab(kobj);
 
-	kfree(s->name);
 	kfree(s);
 }
 
@@ -5318,11 +5310,9 @@ static int sysfs_slab_add(struct kmem_cache *s)
 		return err;
 	}
 	kobject_uevent(&s->kobj, KOBJ_ADD);
-	if (!unmergeable) {
+	if (!unmergeable)
 		/* Setup first alias */
 		sysfs_slab_alias(s, s->name);
-		kfree(name);
-	}
 	return 0;
 }
 
-- 
1.7.7.6

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