From 305347550becd08fdb576df32fc0767842ed71a6 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 19 May 2016 17:14:04 -0700 Subject: [PATCH] mm, page_alloc: reduce cost of fair zone allocation policy retry 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-v1r20 optfair-v1r20 Min alloc-odr0-1 377.00 ( 0.00%) 380.00 ( -0.80%) Min alloc-odr0-2 273.00 ( 0.00%) 273.00 ( 0.00%) Min alloc-odr0-4 226.00 ( 0.00%) 227.00 ( -0.44%) Min alloc-odr0-8 196.00 ( 0.00%) 196.00 ( 0.00%) Min alloc-odr0-16 183.00 ( 0.00%) 183.00 ( 0.00%) Min alloc-odr0-32 175.00 ( 0.00%) 173.00 ( 1.14%) Min alloc-odr0-64 172.00 ( 0.00%) 169.00 ( 1.74%) Min alloc-odr0-128 170.00 ( 0.00%) 169.00 ( 0.59%) Min alloc-odr0-256 183.00 ( 0.00%) 180.00 ( 1.64%) Min alloc-odr0-512 191.00 ( 0.00%) 190.00 ( 0.52%) Min alloc-odr0-1024 199.00 ( 0.00%) 198.00 ( 0.50%) Min alloc-odr0-2048 204.00 ( 0.00%) 204.00 ( 0.00%) Min alloc-odr0-4096 210.00 ( 0.00%) 209.00 ( 0.48%) Min alloc-odr0-8192 213.00 ( 0.00%) 213.00 ( 0.00%) Min alloc-odr0-16384 214.00 ( 0.00%) 214.00 ( 0.00%) The benefit is marginal at best but 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 Acked-by: Vlastimil Babka Cc: Jesper Dangaard Brouer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 8380011..a412493 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2680,12 +2680,10 @@ 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. @@ -2705,13 +2703,16 @@ zonelist_scan: * 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 @@ -2800,18 +2801,13 @@ try_this_zone: * 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; } -- 2.7.4