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Date: Sun, 1 Jan 2017 13:44:51 +0100
From: Grygorii Maistrenko <grygoriimkd@gmail.com>
Subject: [PATCH v2] slub: do not merge cache if slub_debug contains a
 never-merge flag
Message-ID: <20170101124451.GA4740@lp-laptop-d>
References: <20161222235959.GC6871@lp-laptop-d>
 <alpine.DEB.2.20.1612231228340.21172@east.gentwo.org>
 <20161223190023.GA9644@lp-laptop-d>
 <alpine.DEB.2.20.1612241708280.9536@east.gentwo.org>
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Christoph Lameter <cl@linux.com>
Cc: linux-mm@kvack.org, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>

In case CONFIG_SLUB_DEBUG_ON=n, find_mergeable() gets debug features
from commandline but never checks if there are features from the
SLAB_NEVER_MERGE set.
As a result selected by slub_debug caches are always mergeable if they
have been created without a custom constructor set or without one of the
SLAB_* debug features on.

This moves the SLAB_NEVER_MERGE check below the flags update from
commandline to make sure it won't merge the slab cache if one of the
debug features is on.

Signed-off-by: Grygorii Maistrenko <grygoriimkd@gmail.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Acked-by: David Rientjes <rientjes@google.com>
---
 mm/slab_common.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

New in v2:
	- (flags & SLAB_NEVER_MERGE) check is moved down below the flags update
	  as suggested by Christoph Lameter

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 329b03843863..a85a01439490 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -255,7 +255,7 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
 {
 	struct kmem_cache *s;
 
-	if (slab_nomerge || (flags & SLAB_NEVER_MERGE))
+	if (slab_nomerge)
 		return NULL;
 
 	if (ctor)
@@ -266,6 +266,9 @@ struct kmem_cache *find_mergeable(size_t size, size_t align,
 	size = ALIGN(size, align);
 	flags = kmem_cache_flags(size, flags, name, NULL);
 
+	if (flags & SLAB_NEVER_MERGE)
+		return NULL;
+
 	list_for_each_entry_reverse(s, &slab_caches, list) {
 		if (slab_unmergeable(s))
 			continue;
-- 
2.11.0

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