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.

Link: https://lkml.kernel.org/r/eb2fbbeaef2b1714097b9dec457426d682ee0635.1649676424.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 35f6416d29534dc8182ab07f542f13a019554aaf..f97d724b8fc01cef59f42457424539fb7f037d0c 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -471,11 +471,6 @@ 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;