Commit e6cf9e1c authored by Johannes Weiner's avatar Johannes Weiner Committed by Andrew Morton
Browse files

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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: default avatarZi Yan <ziy@nvidia.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarMel Gorman <mgorman@techsingularity.net>
Tested-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Tested-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9cbe97ba

mm/page_alloc.c

+11 −4
Original line number Diff line number Diff line
@@ -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)))

			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);

			}

		}



		/*