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authorDavid Rientjes <rientjes@google.com>2014-04-04 01:48:00 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-04 03:21:01 +0400
commit119d6d59dcc0980dcd581fdadb6b2033b512a473 (patch)
tree1665b6adb48ecf35e458e62c59314b039fdd7fe8
parentf412c97abef71026d8192ca8efca231f1e3906b3 (diff)
downloadlinux-119d6d59dcc0980dcd581fdadb6b2033b512a473.tar.xz
mm, compaction: avoid isolating pinned pages
Page migration will fail for memory that is pinned in memory with, for example, get_user_pages(). In this case, it is unnecessary to take zone->lru_lock or isolating the page and passing it to page migration which will ultimately fail. This is a racy check, the page can still change from under us, but in that case we'll just fail later when attempting to move the page. This avoids very expensive memory compaction when faulting transparent hugepages after pinning a lot of memory with a Mellanox driver. On a 128GB machine and pinning ~120GB of memory, before this patch we see the enormous disparity in the number of page migration failures because of the pinning (from /proc/vmstat): compact_pages_moved 8450 compact_pagemigrate_failed 15614415 0.05% of pages isolated are successfully migrated and explicitly triggering memory compaction takes 102 seconds. After the patch: compact_pages_moved 9197 compact_pagemigrate_failed 7 99.9% of pages isolated are now successfully migrated in this configuration and memory compaction takes less than one second. Signed-off-by: David Rientjes <rientjes@google.com> Acked-by: Hugh Dickins <hughd@google.com> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Rik van Riel <riel@redhat.com> Cc: Greg Thelen <gthelen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/compaction.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 37b3799d948c..212f41c6278b 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -584,6 +584,15 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
continue;
}
+ /*
+ * Migration will fail if an anonymous page is pinned in memory,
+ * so avoid taking lru_lock and isolating it unnecessarily in an
+ * admittedly racy check.
+ */
+ if (!page_mapping(page) &&
+ page_count(page) > page_mapcount(page))
+ continue;
+
/* Check if it is ok to still hold the lock */
locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
locked, cc);