From owner-linux-mm@kvack.org Wed May 11 11:35:30 2011

From: Mel Gorman <mgorman@suse.de>

To: Andrew Morton <akpm@linux-foundation.org>

Subject: [PATCH 3/3] mm: slub: Default slub_max_order to 0

Date: Wed, 11 May 2011 16:29:33 +0100

Message-Id: <1305127773-10570-4-git-send-email-mgorman@suse.de>

To avoid locking and per-cpu overhead, SLUB optimisically uses

high-order allocations up to order-3 by default and falls back to

lower allocations if they fail. While care is taken that the caller

and kswapd take no unusual steps in response to this, there are

further consequences like shrinkers who have to free more objects to

release any memory. There is anecdotal evidence that significant time

is being spent looping in shrinkers with insufficient progress being

made (https://lkml.org/lkml/2011/4/28/361) and keeping kswapd awake.

SLUB is now the default allocator and some bug reports have been

pinned down to SLUB using high orders during operations like

copying large amounts of data. SLUBs use of high-orders benefits

applications that are sized to memory appropriately but this does not

necessarily apply to large file servers or desktops.  This patch

causes SLUB to use order-0 pages like SLAB does by default.

There is further evidence that this keeps kswapd's usage lower

(https://lkml.org/lkml/2011/5/10/383).

Signed-off-by: Mel Gorman <mgorman@suse.de>

---

 Documentation/vm/slub.txt |    2 +-

 mm/slub.c                 |    2 +-

 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt

index 07375e7..778e9fa 100644

--- a/Documentation/vm/slub.txt

+++ b/Documentation/vm/slub.txt

@@ -117,7 +117,7 @@ can be influenced by kernel parameters:

 slub_min_objects=x		(default 4)

 slub_min_order=x		(default 0)

-slub_max_order=x		(default 1)

+slub_max_order=x		(default 0)

 slub_min_objects allows to specify how many objects must at least fit

 into one slab in order for the allocation order to be acceptable.

diff --git a/mm/slub.c b/mm/slub.c

index 1071723..23a4789 100644

--- a/mm/slub.c

+++ b/mm/slub.c

@@ -2198,7 +2198,7 @@ EXPORT_SYMBOL(kmem_cache_free);

  * take the list_lock.

  */

 static int slub_min_order;

-static int slub_max_order = PAGE_ALLOC_COSTLY_ORDER;

+static int slub_max_order;

 static int slub_min_objects;

 /*

-- 

1.7.3.4

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