From 23771235bb569c4999ff077d2c38eaee5763193a Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 28 Jul 2016 15:49:16 -0700 Subject: [PATCH] mm, page_alloc: don't retry initial attempt in slowpath After __alloc_pages_slowpath() sets up new alloc_flags and wakes up kswapd, it first tries get_page_from_freelist() with the new alloc_flags, as it may succeed e.g. due to using min watermark instead of low watermark. It makes sense to to do this attempt before adjusting zonelist based on alloc_flags/gfp_mask, as it's still relatively a fast path if we just wake up kswapd and successfully allocate. This patch therefore moves the initial attempt above the retry label and reorganizes a bit the part below the retry label. We still have to attempt get_page_from_freelist() on each retry, as some allocations cannot do that as part of direct reclaim or compaction, and yet are not allowed to fail (even though they do a WARN_ON_ONCE() and thus should not exist). We can reuse the call meant for ALLOC_NO_WATERMARKS attempt and just set alloc_flags to ALLOC_NO_WATERMARKS if the context allows it. As a side-effect, the attempts from direct reclaim/compaction will also no longer obey watermarks once this is set, but there's little harm in that. Kswapd wakeups are also done on each retry to be safe from potential races resulting in kswapd going to sleep while a process (that may not be able to reclaim by itself) is still looping. Link: http://lkml.kernel.org/r/20160721073614.24395-4-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Acked-by: Mel Gorman Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_alloc.c | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5703f7fca832..a42fa09ee91f 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3510,35 +3510,42 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, */ alloc_flags = gfp_to_alloc_flags(gfp_mask); + if (gfp_mask & __GFP_KSWAPD_RECLAIM) + wake_all_kswapds(order, ac); + + /* + * The adjusted alloc_flags might result in immediate success, so try + * that first + */ + page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); + if (page) + goto got_pg; + + retry: + /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */ if (gfp_mask & __GFP_KSWAPD_RECLAIM) wake_all_kswapds(order, ac); + if (gfp_pfmemalloc_allowed(gfp_mask)) + alloc_flags = ALLOC_NO_WATERMARKS; + /* * Reset the zonelist iterators if memory policies can be ignored. * These allocations are high priority and system rather than user * orientated. */ - if (!(alloc_flags & ALLOC_CPUSET) || gfp_pfmemalloc_allowed(gfp_mask)) { + if (!(alloc_flags & ALLOC_CPUSET) || (alloc_flags & ALLOC_NO_WATERMARKS)) { ac->zonelist = node_zonelist(numa_node_id(), gfp_mask); ac->preferred_zoneref = first_zones_zonelist(ac->zonelist, ac->high_zoneidx, ac->nodemask); } - /* This is the last chance, in general, before the goto nopage. */ + /* Attempt with potentially adjusted zonelist and alloc_flags */ page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); if (page) goto got_pg; - /* Allocate without watermarks if the context allows */ - if (gfp_pfmemalloc_allowed(gfp_mask)) { - - page = get_page_from_freelist(gfp_mask, order, - ALLOC_NO_WATERMARKS, ac); - if (page) - goto got_pg; - } - /* Caller is not willing to reclaim, we can't balance anything */ if (!can_direct_reclaim) { /* -- 2.20.1