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@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/mm/slub.c b/mm/slub.c
index 578f68f3c51f76ed3c2ff21b5ff2545d2ab64c0d..39d39653239b182d26b6edfba1f352e0937476fc 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1390,7 +1390,7 @@ static struct page *get_partial(struct kmem_cache *s, gfp_t flags, int node)
        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);