[PATCH 27/31] mm: page_alloc: cache the last node whose dirty limit is reached

From: Mel Gorman
Date: Fri Jul 01 2016 - 11:42:39 EST


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/1466518566-30034-26-git-send-email-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 d4815a30965b..69ffaadc31ed 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2891,6 +2891,8 @@ 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.
@@ -2923,8 +2925,15 @@ 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