[PATCH v2 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

[Muchun Song]

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 <songmuc...@bytedance.com>
Reviewed-by: Mike Kravetz <mike.krav...@oracle.com>
Acked-by: Yang Shi <shy828...@gmail.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