linux-kernel - [PATCH 4.9 051/109] mm: fix remote numa hits statistics

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Date:   Thu,  7 Dec 2017 13:56:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Michal Hocko <mhocko@...e.com>,
        Jia He <hejianet@...il.com>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Taku Izumi <izumi.taku@...fujitsu.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.9 051/109] mm: fix remote numa hits statistics

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@...e.com>


[ Upstream commit 2df26639e708a88dcc22171949da638a9998f3bc ]

Jia He has noticed that commit 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.

Fixes: b9f00e147f27 ("mm, page_alloc: reduce branches in zone_statistics")
Link: http://lkml.kernel.org/r/20170102153057.9451-2-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@...e.com>
Reported-by: Jia He <hejianet@...il.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz> # with cbmc[1] superpowers
Acked-by: Mel Gorman <mgorman@...e.de>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Taku Izumi <izumi.taku@...fujitsu.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/page_alloc.c |   15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2592,30 +2592,23 @@ int __isolate_free_page(struct page *pag
  * 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
 }