linux-kernel - [PATCH] mm/page_isolation: do not isolate the max order page

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Message-Id: <20201202122114.75316-1-songmuchun@bytedance.com>
Date:   Wed,  2 Dec 2020 20:21:14 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH] mm/page_isolation: do not isolate the max order page

The max order page has no buddy page and never merge to other order.
So isolating and then freeing it is pointless.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/page_isolation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index a254e1f370a3..bddf788f45bf 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -88,7 +88,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 	 */
 	if (PageBuddy(page)) {
 		order = buddy_order(page);
-		if (order >= pageblock_order) {
+		if (order >= pageblock_order && order < MAX_ORDER - 1) {
 			pfn = page_to_pfn(page);
 			buddy_pfn = __find_buddy_pfn(pfn, order);
 			buddy = page + (buddy_pfn - pfn);
-- 
2.11.0