mm: page migration fix PageMlocked on migrated pages (51afb12b) · Commits · 戴 / test

Commit ("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@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Rik van Riel <riel@redhat.com> Acked-by:

Vlastimil Babka <vbabka@suse.cz> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/internal.h

+4 −5

Original line number	Diff line number	Diff line
		@@ -271,20 +271,19 @@ extern unsigned int munlock_vma_page(struct page *page);
		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);
		}
		}

mm/migrate.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -171,6 +171,9 @@ static int remove_migration_pte(struct page new, struct vm_area_struct vma,
		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 newpage, struct page page)
		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
		@@ -1787,7 +1789,6 @@ 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 */
		@@ -1829,6 +1830,7 @@ fail_putback:
		goto fail_putback;
		}

		mlock_migrate_page(new_page, page);
		mem_cgroup_migrate(page, new_page, false);

		page_remove_rmap(page);

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