linux-kernel - [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

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Date:   Mon,  4 Jan 2021 14:58:38 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mike.kravetz@...cle.com, akpm@...ux-foundation.org
Cc:     hillf.zj@...baba-inc.com, n-horiguchi@...jp.nec.com,
        ak@...ux.intel.com, yongjun_wei@...ndmicro.com.cn, mhocko@...e.cz,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

If the refcount is one when it is migrated, it means that the page
was freed from under us. So we are done and do not need to migrate.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/migrate.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 4385f2fb5d18..a6631c4eb6a6 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 		return -ENOSYS;
 	}
 
+	if (page_count(hpage) == 1) {
+		/* page was freed from under us. So we are done. */
+		putback_active_hugepage(hpage);
+		return MIGRATEPAGE_SUCCESS;
+	}
+
 	new_hpage = get_new_page(hpage, private);
 	if (!new_hpage)
 		return -ENOMEM;
-- 
2.11.0