The fair zone allocation policy is not without cost but it can be reduced
slightly. This patch removes an unnecessary local variable, checks the
likely conditions of the fair zone policy first, uses a bool instead of
a flags check and falls through when a remote node is encountered instead
of doing a full restart. The benefit is marginal but it's there
4.6.0-rc2 4.6.0-rc2
decstat-v1r11 optfair-v1r12
Min alloc-odr0-1 382.00 ( 0.00%) 370.00 ( 3.14%)
Min alloc-odr0-2 275.00 ( 0.00%) 271.00 ( 1.45%)
Min alloc-odr0-4 228.00 ( 0.00%) 227.00 ( 0.44%)
Min alloc-odr0-8 199.00 ( 0.00%) 197.00 ( 1.01%)
Min alloc-odr0-16 186.00 ( 0.00%) 182.00 ( 2.15%)
Min alloc-odr0-32 178.00 ( 0.00%) 175.00 ( 1.69%)
Min alloc-odr0-64 174.00 ( 0.00%) 171.00 ( 1.72%)
Min alloc-odr0-128 172.00 ( 0.00%) 169.00 ( 1.74%)
Min alloc-odr0-256 181.00 ( 0.00%) 179.00 ( 1.10%)
Min alloc-odr0-512 193.00 ( 0.00%) 192.00 ( 0.52%)
Min alloc-odr0-1024 200.00 ( 0.00%) 201.00 ( -0.50%)
Min alloc-odr0-2048 206.00 ( 0.00%) 205.00 ( 0.49%)
Min alloc-odr0-4096 212.00 ( 0.00%) 211.00 ( 0.47%)
Min alloc-odr0-8192 215.00 ( 0.00%) 214.00 ( 0.47%)
Min alloc-odr0-16384 215.00 ( 0.00%) 214.00 ( 0.47%)
One of the most important benefits -- avoiding a second search when
falling back to another node is not triggered by this particular test so
the benefit for some corner cases is understated.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 32 ++++++++++++++------------------
1 file changed, 14 insertions(+), 18 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 219e0d05ed88..25a8ab07b287 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2675,12 +2675,10 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
{
struct zoneref *z;
struct zone *zone;
- bool fair_skipped;
- bool zonelist_rescan;
+ bool fair_skipped = false;
+ bool apply_fair = (alloc_flags & ALLOC_FAIR);
zonelist_scan:
- zonelist_rescan = false;
-
/*
* Scan zonelist, looking for a zone with enough free.
* See also __cpuset_node_allowed() comment in kernel/cpuset.c.
@@ -2700,13 +2698,16 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
* page was allocated in should have no effect on the
* time the page has in memory before being reclaimed.
*/
- if (alloc_flags & ALLOC_FAIR) {
- if (!zone_local(ac->preferred_zone, zone))
- break;
+ if (apply_fair) {
if (test_bit(ZONE_FAIR_DEPLETED, &zone->flags)) {
fair_skipped = true;
continue;
}
+ if (!zone_local(ac->preferred_zone, zone)) {
+ if (fair_skipped)
+ goto reset_fair;
+ apply_fair = false;
+ }
}
/*
* When allocating a page cache page for writing, we
@@ -2795,18 +2796,13 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
* include remote zones now, before entering the slowpath and waking
* kswapd: prefer spilling to a remote zone over swapping locally.
*/
- if (alloc_flags & ALLOC_FAIR) {
- alloc_flags &= ~ALLOC_FAIR;
- if (fair_skipped) {
- zonelist_rescan = true;
- reset_alloc_batches(ac->preferred_zone);
- }
- if (nr_online_nodes > 1)
- zonelist_rescan = true;
- }
-
- if (zonelist_rescan)
+ if (fair_skipped) {
+reset_fair:
+ apply_fair = false;
+ fair_skipped = false;
+ reset_alloc_batches(ac->preferred_zone);
goto zonelist_scan;
+ }
return NULL;
}
--
2.6.4
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>