[090/227] mm: page_alloc: avoid merging non-fallbackable pageblocks with others

Commit Message

Andrew Morton March 22, 2022, 9:43 p.m. UTC

From: Zi Yan <[e-mail]>
Subject: mm: page_alloc: avoid merging non-fallbackable pageblocks with others

This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.  It
prepares for the upcoming removal of the MAX_ORDER-1 alignment requirement
for CMA and alloc_contig_range().

MIGRATE_HIGHATOMIC should not merge with other migratetypes like
MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.

Remove MIGRATE_CMA and MIGRATE_ISOLATE from fallbacks list, since they
are never used.

[1] https://lore.kernel.org/linux-mm/[e-mail]/

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Zi Yan <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Acked-by: Mike Rapoport <[e-mail]>
Reviewed-by: Oscar Salvador <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/mmzone.h |   11 +++++++++
 mm/page_alloc.c        |   46 ++++++++++++++++++---------------------
 2 files changed, 33 insertions(+), 24 deletions(-)

Patch

--- a/include/linux/mmzone.h~mm-page_alloc-avoid-merging-non-fallbackable-pageblocks-with-others
+++ a/include/linux/mmzone.h
@@ -83,6 +83,17 @@  static inline bool is_migrate_movable(in
 	return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
 }
 
+/*
+ * Check whether a migratetype can be merged with another migratetype.
+ *
+ * It is only mergeable when it can fall back to other migratetypes for
+ * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
+ */
+static inline bool migratetype_is_mergeable(int mt)
+{
+	return mt < MIGRATE_PCPTYPES;
+}
+
 #define for_each_migratetype_order(order, type) \
 	for (order = 0; order < MAX_ORDER; order++) \
 		for (type = 0; type < MIGRATE_TYPES; type++)
--- a/mm/page_alloc.c~mm-page_alloc-avoid-merging-non-fallbackable-pageblocks-with-others
+++ a/mm/page_alloc.c
@@ -1117,25 +1117,24 @@  continue_merging:
 	}
 	if (order < MAX_ORDER - 1) {
 		/* If we are here, it means order is >= pageblock_order.
-		 * We want to prevent merge between freepages on isolate
-		 * pageblock and normal pageblock. Without this, pageblock
-		 * isolation could cause incorrect freepage or CMA accounting.
+		 * We want to prevent merge between freepages on pageblock
+		 * without fallbacks and normal pageblock. Without this,
+		 * pageblock isolation could cause incorrect freepage or CMA
+		 * accounting or HIGHATOMIC accounting.
 		 *
 		 * We don't want to hit this code for the more frequent
 		 * low-order merging.
 		 */
-		if (unlikely(has_isolate_pageblock(zone))) {
-			int buddy_mt;
+		int buddy_mt;
 
-			buddy_pfn = __find_buddy_pfn(pfn, order);
-			buddy = page + (buddy_pfn - pfn);
-			buddy_mt = get_pageblock_migratetype(buddy);
-
-			if (migratetype != buddy_mt
-					&& (is_migrate_isolate(migratetype) ||
-						is_migrate_isolate(buddy_mt)))
-				goto done_merging;
-		}
+		buddy_pfn = __find_buddy_pfn(pfn, order);
+		buddy = page + (buddy_pfn - pfn);
+		buddy_mt = get_pageblock_migratetype(buddy);
+
+		if (migratetype != buddy_mt
+				&& (!migratetype_is_mergeable(migratetype) ||
+					!migratetype_is_mergeable(buddy_mt)))
+			goto done_merging;
 		max_order = order + 1;
 		goto continue_merging;
 	}
@@ -2479,17 +2478,13 @@  struct page *__rmqueue_smallest(struct z
 /*
  * This array describes the order lists are fallen back to when
  * the free lists for the desirable migrate type are depleted
+ *
+ * The other migratetypes do not have fallbacks.
  */
 static int fallbacks[MIGRATE_TYPES][3] = {
 	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_TYPES },
 	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
 	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_TYPES },
-#ifdef CONFIG_CMA
-	[MIGRATE_CMA]         = { MIGRATE_TYPES }, /* Never used */
-#endif
-#ifdef CONFIG_MEMORY_ISOLATION
-	[MIGRATE_ISOLATE]     = { MIGRATE_TYPES }, /* Never used */
-#endif
 };
 
 #ifdef CONFIG_CMA
@@ -2795,8 +2790,8 @@  static void reserve_highatomic_pageblock
 
 	/* Yoink! */
 	mt = get_pageblock_migratetype(page);
-	if (!is_migrate_highatomic(mt) && !is_migrate_isolate(mt)
-	    && !is_migrate_cma(mt)) {
+	/* Only reserve normal pageblocks (i.e., they can merge with others) */
+	if (migratetype_is_mergeable(mt)) {
 		zone->nr_reserved_highatomic += pageblock_nr_pages;
 		set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
 		move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
@@ -3545,8 +3540,11 @@  int __isolate_free_page(struct page *pag
 		struct page *endpage = page + (1 << order) - 1;
 		for (; page < endpage; page += pageblock_nr_pages) {
 			int mt = get_pageblock_migratetype(page);
-			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
-			    && !is_migrate_highatomic(mt))
+			/*
+			 * Only change normal pageblocks (i.e., they can merge
+			 * with others)
+			 */
+			if (migratetype_is_mergeable(mt))
 				set_pageblock_migratetype(page,
 							  MIGRATE_MOVABLE);
 		}