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

Michal Hocko
2017-01-02T15:31:27Z

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")
Acked-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz> # with cbmc[1] superpowers
Signed-off-by: Michal Hocko <mhocko@suse.com>

[1] http://paulmck.livejournal.com/38997.html
---
mm/page_alloc.c | 15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f6d5b73e1d7c..e2a44950a685 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2583,30 +2583,23 @@ 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)) {
+ if (z->node != numa_node_id())
local_stat = NUMA_OTHER;
- local_nid = preferred_zone->node;
- }

- if (z->node == local_nid) {
+ if (z->node == preferred_zone->node)
__inc_zone_state(z, NUMA_HIT);
- __inc_zone_state(z, local_stat);
- } else {
+ else {
__inc_zone_state(z, NUMA_MISS);
__inc_zone_state(preferred_zone, NUMA_FOREIGN);
}
+ __inc_zone_state(z, local_stat);
#endif
}

--
2.11.0