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From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
	Jia He <hejianet@gmail.com>, Andi Kleen <ak@linux.intel.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH 1/2] mm: fix remote numa hits statistics
Date: Mon,  2 Jan 2017 16:30:56 +0100
Message-ID: <20170102153057.9451-2-mhocko@kernel.org> (raw)
In-Reply-To: <20170102153057.9451-1-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")
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

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  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-02 15:30 [PATCH 0/2] numa node stats alternative fix Michal Hocko
2017-01-02 15:30 ` Michal Hocko [this message]
2017-01-02 15:30 ` [PATCH 2/2] mm: get rid of __GFP_OTHER_NODE Michal Hocko
  -- strict thread matches above, loose matches on Subject: below --
2016-12-21  7:57 [PATCH RFC 1/1] mm, page_alloc: fix incorrect zone_statistics data Michal Hocko
2016-12-21  8:06 ` [PATCH 1/2] mm: fix remote numa hits statistics Michal Hocko
2016-12-29 11:46   ` Mel Gorman
2016-12-29 12:28     ` Michal Hocko
2017-01-02 14:16   ` Vlastimil Babka
2017-01-02 14:46     ` Michal Hocko
2017-01-02 15:07       ` Vlastimil Babka

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