mm: page_alloc: cache the last node whose dirty limit is reached

If a page is about to be dirtied then the page allocator attempts to
limit the total number of dirty pages that exists in any given zone.
The call to node_dirty_ok is expensive so this patch records if the last
pgdat examined hit the dirty limits.  In some cases, this reduces the
number of calls to node_dirty_ok().

Link: http://lkml.kernel.org/r/1467970510-21195-31-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.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 1dd0f1f218db4ed559274cb4d52771696ca499c5..7427e0e8364243b9269e4890cc3f2498e65b661e 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2848,6 +2848,8 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 {
        struct zoneref *z = ac->preferred_zoneref;
        struct zone *zone;
+       struct pglist_data *last_pgdat_dirty_limit = NULL;
+
        /*
         * Scan zonelist, looking for a zone with enough free.
         * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
@@ -2880,8 +2882,15 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
                 * will require awareness of nodes in the
                 * dirty-throttling and the flusher threads.
                 */
-               if (ac->spread_dirty_pages && !node_dirty_ok(zone->zone_pgdat))
-                       continue;
+               if (ac->spread_dirty_pages) {
+                       if (last_pgdat_dirty_limit == zone->zone_pgdat)
+                               continue;
+
+                       if (!node_dirty_ok(zone->zone_pgdat)) {
+                               last_pgdat_dirty_limit = zone->zone_pgdat;
+                               continue;
+                       }
+               }
 
                mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
                if (!zone_watermark_fast(zone, order, mark,