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mm: page migration fix PageMlocked on migrated pages

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Commit e6c509f854 ("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 <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Rik van Riel <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Hugh Dickins 2015-11-05 18:49:37 -08:00 • committed by Linus Torvalds
commit 51afb12ba8
2 changed files with 8 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

6
mm/migrate.c
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@ -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);