From 66987218154918a6341a3e3eeeee58110a69e0bb Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Tue, 6 Jan 2026 12:52:36 +0100 Subject: [PATCH] mm/page_alloc: ignore the exact initial compaction result Patch series "tweaks for __alloc_pages_slowpath()", v3. This patch (of 3): For allocations that are of costly order and __GFP_NORETRY (and can perform compaction) we attempt direct compaction first. If that fails, we continue with a single round of direct reclaim+compaction (as for other __GFP_NORETRY allocations, except the compaction is of lower priority), with two exceptions that fail immediately: - __GFP_THISNODE is specified, to prevent zone_reclaim_mode-like behavior for e.g. THP page faults - compaction failed because it was deferred (i.e. has been failing recently so further attempts are not done for a while) or skipped, which means there are insufficient free base pages to defragment to begin with Upon closer inspection, the second condition has a somewhat flawed reasoning. If there are not enough base pages and reclaim could create them, we instead fail. When there are enough base pages and compaction has already ran and failed, we proceed and hope that reclaim and the subsequent compaction attempt will succeed. But it's unclear why they should and whether it will be as inexpensive as intended. It might make therefore more sense to just fail unconditionally after the initial compaction attempt. However that would change the semantics of __GFP_NORETRY to attempt reclaim at least once. Alternatively we can remove the compaction result checks and proceed with the single reclaim and (lower priority) compaction attempt, leaving only the __GFP_THISNODE exception for failing immediately. Link: https://lkml.kernel.org/r/20260106-thp-thisnode-tweak-v3-0-f5d67c21a193@suse.cz Link: https://lkml.kernel.org/r/20260106-thp-thisnode-tweak-v3-1-f5d67c21a193@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Cc: Brendan Jackman Cc: David Hildenbrand (Red Hat) Cc: David Rientjes Cc: Johannes Weiner Cc: Joshua Hahn 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 | 34 ++++++---------------------------- 1 file changed, 6 insertions(+), 28 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index bc3ee3102b19a..8e6d2e61374ae 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4797,44 +4797,22 @@ restart: * includes some THP page fault allocations */ if (costly_order && (gfp_mask & __GFP_NORETRY)) { - /* - * If allocating entire pageblock(s) and compaction - * failed because all zones are below low watermarks - * or is prohibited because it recently failed at this - * order, fail immediately unless the allocator has - * requested compaction and reclaim retry. - * - * Reclaim is - * - potentially very expensive because zones are far - * below their low watermarks or this is part of very - * bursty high order allocations, - * - not guaranteed to help because isolate_freepages() - * may not iterate over freed pages as part of its - * linear scan, and - * - unlikely to make entire pageblocks free on its - * own. - */ - if (compact_result == COMPACT_SKIPPED || - compact_result == COMPACT_DEFERRED) - goto nopage; - /* * THP page faults may attempt local node only first, * but are then allowed to only compact, not reclaim, * see alloc_pages_mpol(). * - * Compaction can fail for other reasons than those - * checked above and we don't want such THP allocations - * to put reclaim pressure on a single node in a - * situation where other nodes might have plenty of - * available memory. + * Compaction has failed above and we don't want such + * THP allocations to put reclaim pressure on a single + * node in a situation where other nodes might have + * plenty of available memory. */ if (gfp_mask & __GFP_THISNODE) goto nopage; /* - * Looks like reclaim/compaction is worth trying, but - * sync compaction could be very expensive, so keep + * Proceed with single round of reclaim/compaction, but + * since sync compaction could be very expensive, keep * using async compaction. */ compact_priority = INIT_COMPACT_PRIORITY; -- 2.47.3