netdev - slub numa: Fix rare allocation from unexpected node

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Message-ID: <alpine.DEB.2.00.1007261040430.5438@router.home>
Date:	Mon, 26 Jul 2010 10:41:14 -0500 (CDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	linux-mm@...ck.org, jamal <hadi@...erus.ca>, netdev@...r.kernel.org
Subject: slub numa: Fix rare allocation from unexpected node

Subject: slub numa: Fix rare allocation from unexpected node

The network developers have seen sporadic allocations resulting in objects
coming from unexpected NUMA nodes despite asking for objects from a
specific node.

This is due to get_partial() calling get_any_partial() if partial
slabs are exhausted for a node even if a node was specified and therefore
one would expect allocations only from the specified node.

get_any_partial() sporadically may return a slab from a foreign
node to gradually reduce the size of partial lists on remote nodes
and thereby reduce total memory use for a slab cache.

The behavior is controlled by the remote_defrag_ratio of each cache.

Strictly speaking this is permitted behavior since __GFP_THISNODE was
not specified for the allocation but it is certain surprising.

This patch makes sure that the remote defrag behavior only occurs
if no node was specified.

Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>

---
 mm/slub.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-07-23 09:24:11.000000000 -0500
+++ linux-2.6/mm/slub.c	2010-07-23 09:25:15.000000000 -0500
@@ -1390,7 +1390,7 @@ static struct page *get_partial(struct k
 	int searchnode = (node == -1) ? numa_node_id() : node;

 	page = get_partial_node(get_node(s, searchnode));
-	if (page || (flags & __GFP_THISNODE))
+	if (page || node != -1)
 		return page;

 	return get_any_partial(s, flags);
--
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