mm: page_alloc: do not update zlc unless the zlc is active

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@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d88d675847658b3d80e4b24a194e30459cb45446..8e766241cf566cf6f8a72b94e560f546858ed0f2 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2035,7 +2035,7 @@ try_this_zone:
                if (page)
                        break;
 this_zone_full:
-               if (IS_ENABLED(CONFIG_NUMA))
+               if (IS_ENABLED(CONFIG_NUMA) && zlc_active)
                        zlc_mark_zone_full(zonelist, z);
        }