From 2c4c3e29897d43c431b1cf9432fb66977f262ac2 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Tue, 6 Jan 2026 12:52:38 +0100 Subject: [PATCH] mm/page_alloc: simplify __alloc_pages_slowpath() flow The actions done before entering the main retry loop include waking up kswapds and an allocation attempt with the precise alloc_flags. Then in the loop we keep waking up kswapds, and we retry the allocation with flags potentially further adjusted by being allowed to use reserves (due to e.g. becoming an OOM killer victim). We can adjust the retry loop to keep only one instance of waking up kswapds and allocation attempt. Introduce the can_retry_reserves variable for retrying once when we become eligible for reserves. It is still useful not to evaluate reserve_flags immediately for the first allocation attempt, because it's better to first try succeed in a non-preferred zone above the min watermark before allocating immediately from the preferred zone below min watermark. Additionally move the cpuset update checks introduced by e05741fb10c3 ("mm/page_alloc.c: avoid infinite retries caused by cpuset race") further down the retry loop. It's enough to do the checks only before reaching any potentially infinite 'goto retry;' loop. There should be no meaningful functional changes. The change of exact moments the retry for reserves and cpuset updates are checked should not result in different outomes modulo races with concurrent allocator activity. Link: https://lkml.kernel.org/r/20260106-thp-thisnode-tweak-v3-3-f5d67c21a193@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Joshua Hahn Cc: Brendan Jackman Cc: David Hildenbrand (Red Hat) Cc: David Rientjes Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Pedro Falcato Cc: Suren Baghdasaryan Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/page_alloc.c | 41 +++++++++++++++++++++++------------------ 1 file changed, 23 insertions(+), 18 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 848c5c93ccb5e..f7d777921f05f 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4708,6 +4708,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, unsigned int zonelist_iter_cookie; int reserve_flags; bool compact_first = false; + bool can_retry_reserves = true; if (unlikely(nofail)) { /* @@ -4775,6 +4776,8 @@ restart: goto nopage; } +retry: + /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */ if (alloc_flags & ALLOC_KSWAPD) wake_all_kswapds(order, gfp_mask, ac); @@ -4786,19 +4789,6 @@ restart: if (page) goto got_pg; -retry: - /* - * Deal with possible cpuset update races or zonelist updates to avoid - * infinite retries. - */ - if (check_retry_cpuset(cpuset_mems_cookie, ac) || - check_retry_zonelist(zonelist_iter_cookie)) - goto restart; - - /* Ensure kswapd doesn't accidentally go to sleep as long as we loop */ - if (alloc_flags & ALLOC_KSWAPD) - wake_all_kswapds(order, gfp_mask, ac); - reserve_flags = __gfp_pfmemalloc_flags(gfp_mask); if (reserve_flags) alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, reserve_flags) | @@ -4813,12 +4803,18 @@ retry: ac->nodemask = NULL; ac->preferred_zoneref = first_zones_zonelist(ac->zonelist, ac->highest_zoneidx, ac->nodemask); - } - /* Attempt with potentially adjusted zonelist and alloc_flags */ - page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac); - if (page) - goto got_pg; + /* + * The first time we adjust anything due to being allowed to + * ignore memory policies or watermarks, retry immediately. This + * allows us to keep the first allocation attempt optimistic so + * it can succeed in a zone that is still above watermarks. + */ + if (can_retry_reserves) { + can_retry_reserves = false; + goto retry; + } + } /* Caller is not willing to reclaim, we can't balance anything */ if (!can_direct_reclaim) @@ -4881,6 +4877,15 @@ retry: !(gfp_mask & __GFP_RETRY_MAYFAIL))) goto nopage; + /* + * Deal with possible cpuset update races or zonelist updates to avoid + * infinite retries. No "goto retry;" can be placed above this check + * unless it can execute just once. + */ + if (check_retry_cpuset(cpuset_mems_cookie, ac) || + check_retry_zonelist(zonelist_iter_cookie)) + goto restart; + if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags, did_some_progress > 0, &no_progress_loops)) goto retry; -- 2.47.3