linux-kernel - [PATCH] mm: migrate: Simplify the refcount validation when migrating hugetlb mapping

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Message-Id: <eb2fbbeaef2b1714097b9dec457426d682ee0635.1649676424.git.baolin.wang@linux.alibaba.com>
Date:   Mon, 11 Apr 2022 19:34:30 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org
Cc:     willy@...radead.org, baolin.wang@...ux.alibaba.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm: migrate: Simplify the refcount validation when migrating hugetlb mapping

There is no need to validate the hugetlb page's refcount before trying
to freeze the hugetlb page's expected refcount, instead we can just
rely on the page_ref_freeze() to simplify the validation.

Moreover we are always under the page lock when migrating the hugetlb
page mapping, which means nowhere else can remove it from the page cache,
so we can remove the xas_load() validation under the i_pages lock.

Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Matthew Wilcox <willy@...radead.org>
---
 mm/migrate.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index a3d8c2b..b267827 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -477,11 +477,6 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 
 	xas_lock_irq(&xas);
 	expected_count = 2 + page_has_private(page);
-	if (page_count(page) != expected_count || xas_load(&xas) != page) {
-		xas_unlock_irq(&xas);
-		return -EAGAIN;
-	}
-
 	if (!page_ref_freeze(page, expected_count)) {
 		xas_unlock_irq(&xas);
 		return -EAGAIN;
-- 
1.8.3.1