Commit e6c509f85455 ("mm: use clear_page_mlock() in page_remove_rmap()") in v3.7 inadvertently made mlock_migrate_page() impotent: page migration unmaps the page from userspace before migrating, and that commit clears PageMlocked on the final unmap, leaving mlock_migrate_page() with nothing to do. Not a serious bug, the next attempt at reclaiming the page would fix it up; but a betrayal of page migration's intent - the new page ought to emerge as PageMlocked. I don't see how to fix it for mlock_migrate_page() itself; but easily fixed in remove_migration_pte(), by calling mlock_vma_page() when the vma is VM_LOCKED - under pte lock as in try_to_unmap_one(). Delete mlock_migrate_page()? Not quite, it does still serve a purpose for migrate_misplaced_transhuge_page(): where we could replace it by a test, clear_page_mlock(), mlock_vma_page() sequence; but would that be an improvement? mlock_migrate_page() is fairly lean, and let's make it leaner by skipping the irq save/restore now clearly not needed. Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> --- mm/internal.h | 9 ++++----- mm/migrate.c | 6 ++++-- 2 files changed, 8 insertions(+), 7 deletions(-) --- migrat.orig/mm/internal.h 2015-09-12 18:30:20.841039780 -0700 +++ migrat/mm/internal.h 2015-10-18 17:53:11.061322013 -0700 @@ -271,20 +271,19 @@ extern unsigned int munlock_vma_page(str extern void clear_page_mlock(struct page *page); /* - * mlock_migrate_page - called only from migrate_page_copy() to - * migrate the Mlocked page flag; update statistics. + * mlock_migrate_page - called only from migrate_misplaced_transhuge_page() + * (because that does not go through the full procedure of migration ptes): + * to migrate the Mlocked page flag; update statistics. */ static inline void mlock_migrate_page(struct page *newpage, struct page *page) { if (TestClearPageMlocked(page)) { - unsigned long flags; int nr_pages = hpage_nr_pages(page); - local_irq_save(flags); + /* Holding pmd lock, no change in irq context: __mod is safe */ __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages); SetPageMlocked(newpage); __mod_zone_page_state(page_zone(newpage), NR_MLOCK, nr_pages); - local_irq_restore(flags); } } --- migrat.orig/mm/migrate.c 2015-10-04 10:47:52.469445854 -0700 +++ migrat/mm/migrate.c 2015-10-18 17:53:11.062322014 -0700 @@ -171,6 +171,9 @@ static int remove_migration_pte(struct p else page_add_file_rmap(new); + if (vma->vm_flags & VM_LOCKED) + mlock_vma_page(new); + /* No need to invalidate - it was non-present before */ update_mmu_cache(vma, addr, ptep); unlock: @@ -537,7 +540,6 @@ void migrate_page_copy(struct page *newp cpupid = page_cpupid_xchg_last(page, -1); page_cpupid_xchg_last(newpage, cpupid); - mlock_migrate_page(newpage, page); ksm_migrate_page(newpage, page); /* * Please do not reorder this without considering how mm/ksm.c's @@ -1786,7 +1788,6 @@ fail_putback: SetPageActive(page); if (TestClearPageUnevictable(new_page)) SetPageUnevictable(page); - mlock_migrate_page(page, new_page); unlock_page(new_page); put_page(new_page); /* Free it */ @@ -1828,6 +1829,7 @@ fail_putback: goto fail_putback; } + mlock_migrate_page(new_page, page); mem_cgroup_migrate(page, new_page, false); page_remove_rmap(page); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>