[PATCH 25/27] mm: page_alloc: Cache the last node whose dirty limit is reached

Mel Gorman
2016-06-09T18:09:32Z

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().

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 17fa3f361f01..7c6c18a314a1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2853,6 +2853,8 @@ 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.
@@ -2885,8 +2887,15 @@ 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,
--
2.6.4