[PATCH 1/2] mm: fix remote numa hits statistics

[Michal Hocko <mhocko@kernel.org>]

From: Michal Hocko <mhocko@suse.com>

Jia He has noticed that b9f00e147f27 ("mm, page_alloc: reduce branches
in zone_statistics") has an unintentional side effect that remote node
allocation requests are accounted as NUMA_MISS rathat than NUMA_HIT and
NUMA_OTHER if such a request doesn't use __GFP_OTHER_NODE. There are
many of these potentially because the flag is used very rarely while
we have many users of __alloc_pages_node.

Fix this by simply ignoring __GFP_OTHER_NODE (it can be removed in a
follow up patch) and treat all allocations that were satisfied from the
preferred zone's node as NUMA_HITS because this is the same node we
requested the allocation from in most cases. If this is not the local
node then we just account it as NUMA_OTHER rather than NUMA_LOCAL.

One downsize would be that an allocation request for a node which is
outside of the mempolicy nodemask would be reported as a hit which is a
bit weird but that was the case before b9f00e147f27 already.

Reported-by: Jia He <hejianet@gmail.com>
Fixes: b9f00e147f27 ("mm, page_alloc: reduce branches in zone_statistics")
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/page_alloc.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f6d5b73e1d7c..506946a902c5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2583,25 +2583,17 @@ int __isolate_free_page(struct page *page, unsigned int order)
  * Update NUMA hit/miss statistics
  *
  * Must be called with interrupts disabled.
- *
- * When __GFP_OTHER_NODE is set assume the node of the preferred
- * zone is the local node. This is useful for daemons who allocate
- * memory on behalf of other processes.
  */
 static inline void zone_statistics(struct zone *preferred_zone, struct zone *z,
 								gfp_t flags)
 {
 #ifdef CONFIG_NUMA
-	int local_nid = numa_node_id();
-	enum zone_stat_item local_stat = NUMA_LOCAL;
-
-	if (unlikely(flags & __GFP_OTHER_NODE)) {
-		local_stat = NUMA_OTHER;
-		local_nid = preferred_zone->node;
-	}
+	if (z->node == preferred_zone->node) {
+		enum zone_stat_item local_stat = NUMA_LOCAL;
 
-	if (z->node == local_nid) {
 		__inc_zone_state(z, NUMA_HIT);
+		if (z->node != numa_node_id())
+			local_stat = NUMA_OTHER;
 		__inc_zone_state(z, local_stat);
 	} else {
 		__inc_zone_state(z, NUMA_MISS);
-- 
2.10.2

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>