diff mbox series

[03/10] mm: page_alloc: fix up block types when merging compatible blocks

Message ID 20240320180429.678181-4-hannes@cmpxchg.org (mailing list archive)
State New
Headers show
Series mm: page_alloc: freelist migratetype hygiene | expand

Commit Message

Johannes Weiner March 20, 2024, 6:02 p.m. UTC 
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.

v2:
- remove spurious change_pageblock_range() move (Zi Yan)

Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Tested-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/page_alloc.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 994e4f790e92..4529893d9f04 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -785,10 +785,17 @@  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);
+			}
 		}
 
 		/*