From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: migrate: do not migrate HugeTLB page whose refcount is one All pages isolated for the migration have an elevated reference count and therefore seeing a reference count equal to 1 means that the last user of the page has dropped the reference and the page has became unused and there doesn't make much sense to migrate it anymore. This has been done for regular pages and this patch does the same for hugetlb pages. Although the likelihood of the race is rather small for hugetlb pages it makes sense the two code paths in sync. Link: https://lkml.kernel.org/r/20210115124942.46403-2-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Yang Shi <shy828301@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/migrate.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/migrate.c~mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one +++ a/mm/migrate.c @@ -1280,6 +1280,12 @@ static int unmap_and_move_huge_page(new_ 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; _
