[PATCH 68/97] mm: page_alloc: do not update zlc unless the zlc is active

From: Mel Gorman
Date: Thu Aug 28 2014 - 14:48:22 EST

commit 65bb371984d6a2c909244eb749e482bb40b72e36 upstream.

The zlc is used on NUMA machines to quickly skip over zones that are full.
However it is always updated, even for the first zone scanned when the
zlc might not even be active. As it's a write to a bitmap that
potentially bounces cache line it's deceptively expensive and most
machines will not care. Only update the zlc if it was active.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7139ed7..2834c31 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2034,7 +2034,7 @@ try_this_zone:
if (page)
+ if (IS_ENABLED(CONFIG_NUMA) && zlc_active)
zlc_mark_zone_full(zonelist, z);


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/