From e6cf9e1c4cde8a53385423ecb8ca581097f42e02 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Wed, 20 Mar 2024 14:02:08 -0400 Subject: [PATCH] mm: page_alloc: fix up block types when merging compatible blocks The buddy allocator coalesces compatible blocks during freeing, but it doesn't update the types of the subblocks to match. When an allocation later breaks the chunk down again, its pieces will be put on freelists of the wrong type. This encourages incompatible page mixing (ask for one type, get another), and thus long-term fragmentation. Update the subblocks when merging a larger chunk, such that a later expand() will maintain freelist type hygiene. Link: https://lkml.kernel.org/r/20240320180429.678181-4-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Reviewed-by: Zi Yan Reviewed-by: Vlastimil Babka Acked-by: Mel Gorman Tested-by: "Huang, Ying" Tested-by: Baolin Wang Cc: David Hildenbrand Signed-off-by: Andrew Morton --- mm/page_alloc.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5fa3d534df2f..2c03336def76 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -786,10 +786,17 @@ static inline void __free_one_page(struct page *page, */ int buddy_mt = get_pfnblock_migratetype(buddy, buddy_pfn); - if (migratetype != buddy_mt - && (!migratetype_is_mergeable(migratetype) || - !migratetype_is_mergeable(buddy_mt))) - goto done_merging; + if (migratetype != buddy_mt) { + if (!migratetype_is_mergeable(migratetype) || + !migratetype_is_mergeable(buddy_mt)) + goto done_merging; + /* + * Match buddy type. This ensures that + * an expand() down the line puts the + * sub-blocks on the right freelists. + */ + set_pageblock_migratetype(buddy, migratetype); + } } /*