mm: page_alloc: simplify pageblock migratetype check in __free_one_page()

Move pageblock migratetype check code in the while loop to simplify the
logic. It also saves redundant buddy page checking code.

Link: https://lkml.kernel.org/r/20220401230804.1658207-1-zi.yan@sent.com
Link: https://lore.kernel.org/linux-mm/27ff69f9-60c5-9e59-feb2-295250077551@suse.cz/Signed-off-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_alloc.c

@@ -1053,7 +1053,6 @@ static inline void __free_one_page(struct page *page,
 		int migratetype, fpi_t fpi_flags)
 {
 	struct capture_control *capc = task_capc(zone);
-	unsigned int max_order = pageblock_order;
 	unsigned long buddy_pfn;
 	unsigned long combined_pfn;
 	struct page *buddy;
@@ -1069,8 +1068,7 @@ static inline void __free_one_page(struct page *page,
 	VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page);
 	VM_BUG_ON_PAGE(bad_range(zone, page), page);
 
-continue_merging:
-	while (order < max_order) {
+	while (order < MAX_ORDER - 1) {
 		if (compaction_capture(capc, page, order, migratetype)) {
 			__mod_zone_freepage_state(zone, -(1 << order),
 								migratetype);
@@ -1081,6 +1079,22 @@ static inline void __free_one_page(struct page *page,
 
 		if (!page_is_buddy(page, buddy, order))
 			goto done_merging;
+
+		if (unlikely(order >= pageblock_order)) {
+			/*
+			 * 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.
+			 */
+			int buddy_mt = get_pageblock_migratetype(buddy);
+
+			if (migratetype != buddy_mt
+					&& (!migratetype_is_mergeable(migratetype) ||
+						!migratetype_is_mergeable(buddy_mt)))
+				goto done_merging;
+		}
+
 		/*
 		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
 		 * merge with it and move up one order.
@@ -1094,32 +1108,6 @@ static inline void __free_one_page(struct page *page,
 		pfn = combined_pfn;
 		order++;
 	}
-	if (order < MAX_ORDER - 1) {
-		/* If we are here, it means order is >= pageblock_order.
-		 * 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.
-		 */
-		int buddy_mt;
-
-		buddy_pfn = __find_buddy_pfn(pfn, order);
-		buddy = page + (buddy_pfn - pfn);
-
-		if (!page_is_buddy(page, buddy, order))
-			goto done_merging;
-		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;
-	}
 
 done_merging:
 	set_buddy_order(page, order);