From 5dab29113ca56335c78be3f98bf5ddf2ef8eb6a6 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Wed, 4 Jun 2014 16:10:14 -0700 Subject: [PATCH] mm: page_alloc: take the ALLOC_NO_WATERMARK check out of the fast path ALLOC_NO_WATERMARK is set in a few cases. Always by kswapd, always for __GFP_MEMALLOC, sometimes for swap-over-nfs, tasks etc. Each of these cases are relatively rare events but the ALLOC_NO_WATERMARK check is an unlikely branch in the fast path. This patch moves the check out of the fast path and after it has been determined that the watermarks have not been met. This helps the common fast path at the cost of making the slow path slower and hitting kswapd with a performance cost. It's a reasonable tradeoff. Signed-off-by: Mel Gorman Acked-by: Johannes Weiner Reviewed-by: Rik van Riel Cc: Vlastimil Babka Cc: Jan Kara Cc: Michal Hocko Cc: Hugh Dickins Cc: Dave Hansen Cc: Theodore Ts'o Cc: "Paul E. McKenney" Cc: Oleg Nesterov Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 30f327a720fd..485932c577e7 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1937,9 +1937,6 @@ zonelist_scan: (alloc_flags & ALLOC_CPUSET) && !cpuset_zone_allowed_softwall(zone, gfp_mask)) continue; - BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); - if (unlikely(alloc_flags & ALLOC_NO_WATERMARKS)) - goto try_this_zone; /* * Distribute pages in proportion to the individual * zone size to ensure fair page aging. The zone a @@ -1986,6 +1983,11 @@ zonelist_scan: classzone_idx, alloc_flags)) { int ret; + /* Checked here to keep the fast path fast */ + BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK); + if (alloc_flags & ALLOC_NO_WATERMARKS) + goto try_this_zone; + if (IS_ENABLED(CONFIG_NUMA) && !did_zlc_setup && nr_online_nodes > 1) { /* -- 2.20.1