linux-kernel - [RFC PATCH 15/26] mm: compaction: simplify free block check in suitable_migration

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Date:   Tue, 18 Apr 2023 15:13:02 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     linux-mm@...ck.org
Cc:     Kaiyang Zhao <kaiyang2@...cmu.edu>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [RFC PATCH 15/26] mm: compaction: simplify free block check in suitable_migration_target()

Free page blocks are now marked MIGRATE_FREE. Consult that directly.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/compaction.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index a2280001eea3..b9eed0d43403 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1281,22 +1281,17 @@ static bool suitable_migration_source(struct compact_control *cc,
 static bool suitable_migration_target(struct compact_control *cc,
 							struct page *page)
 {
+	int mt = get_pageblock_migratetype(page);
+
 	/* If the page is a large free page, then disallow migration */
-	if (PageBuddy(page)) {
-		/*
-		 * We are checking page_order without zone->lock taken. But
-		 * the only small danger is that we skip a potentially suitable
-		 * pageblock, so it's not worth to check order for valid range.
-		 */
-		if (buddy_order_unsafe(page) >= pageblock_order)
-			return false;
-	}
+	if (mt == MIGRATE_FREE)
+		return false;
 
 	if (cc->ignore_block_suitable)
 		return true;
 
 	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
-	if (is_migrate_movable(get_pageblock_migratetype(page)))
+	if (is_migrate_movable(mt))
 		return true;
 
 	/* Otherwise skip the block */
-- 
2.39.2