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...
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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));