linux-kernel - [PATCH v3 1/2] mm: page_alloc: simplify pageblock migratetype check in __free_one

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Date:   Fri,  1 Apr 2022 19:08:03 -0400
From:   Zi Yan <zi.yan@...t.com>
To:     linux-mm@...ck.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Zi Yan <ziy@...dia.com>
Subject: [PATCH v3 1/2] mm: page_alloc: simplify pageblock migratetype check in __free_one_page().

From: Zi Yan <ziy@...dia.com>

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

Suggested-by: Vlastimil Babka <vbabka@...e.cz>
Link: https://lore.kernel.org/linux-mm/27ff69f9-60c5-9e59-feb2-295250077551@suse.cz/
Signed-off-by: Zi Yan <ziy@...dia.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/page_alloc.c | 46 +++++++++++++++++-----------------------------
 1 file changed, 17 insertions(+), 29 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 856473e54155..2ea106146686 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1054,7 +1054,6 @@ 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;
@@ -1070,8 +1069,7 @@ 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);
@@ -1082,6 +1080,22 @@ 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.
@@ -1095,32 +1109,6 @@ 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);
-- 
2.35.1