From: Yang Shi <shy828301@gmail.com> mainline inclusion from mainline-v5.14-rc1 commit 662aeea7536d84d7e1d01739694e4748ba294ce0 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IAFONL CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The generic migration path will check refcount, so no need check refcount here. But the old code actually prevents from migrating shared THP (mapped by multiple processes), so bail out early if mapcount is > 1 to keep the behavior. Link: https://lkml.kernel.org/r/20210518200801.7413-7-shy828301@gmail.com Signed-off-by: Yang Shi <shy828301@gmail.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Nanyong Sun <sunnanyong@huawei.com> --- mm/migrate.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index 33badf35219e..3f5b217d5af1 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2107,6 +2107,10 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page) VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page); + /* Do not migrate THP mapped by multiple processes */ + if (PageTransHuge(page) && total_mapcount(page) > 1) + return 0; + /* Avoid migrating to a node that is nearly full */ if (!migrate_balanced_pgdat(pgdat, compound_nr(page))) return 0; @@ -2117,18 +2121,6 @@ static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page) if (isolate_lru_page(page)) return 0; - /* - * migrate_misplaced_transhuge_page() skips page migration's usual - * check on page_count(), so we must do it here, now that the page - * has been isolated: a GUP pin, or any other pin, prevents migration. - * The expected page count is 3: 1 for page's mapcount and 1 for the - * caller's pin and 1 for the reference taken by isolate_lru_page(). - */ - if (PageTransHuge(page) && page_count(page) != 3) { - putback_lru_page(page); - return 0; - } - page_lru = page_is_file_lru(page); mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru, thp_nr_pages(page)); -- 2.25.1