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mm/munlock: page migration needs mlock pagevec drained

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Page migration of a VM_LOCKED page tends to fail, because when the old
page is unmapped, it is put on the mlock pagevec with raised refcount,
which then fails the freeze.

At first I thought this would be fixed by a local mlock_page_drain() at
the upper rmap_walk() level - which would have nicely batched all the
munlocks of that page; but tests show that the task can too easily move
to another cpu, leaving pagevec residue behind which fails the migration.

So try_to_migrate_one() drain the local pagevec after page_remove_rmap()
from a VM_LOCKED vma; and do the same in try_to_unmap_one(), whose
TTU_IGNORE_MLOCK users would want the same treatment; and do the same
in remove_migration_pte() - not important when successfully inserting
a new page, but necessary when hoping to retry after failure.

Any new pagevec runs the risk of adding a new way of stranding, and we
might discover other corners where mlock_page_drain() or lru_add_drain()
would now help.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
This commit is contained in:
Hugh Dickins 2022-02-14 18:38:47 -08:00 committed by Matthew Wilcox (Oracle)
parent 2fbb0c10d1
commit b74355078b
2 changed files with 6 additions and 0 deletions
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2
mm/migrate.c
View file

@ -251,6 +251,8 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
page_add_file_rmap(new, vma, false);
set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
}
if (vma->vm_flags & VM_LOCKED)
mlock_page_drain(smp_processor_id());
/* No need to invalidate - it was non-present before */
update_mmu_cache(vma, pvmw.address, pvmw.pte);

4
mm/rmap.c
View file

@ -1656,6 +1656,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
* See Documentation/vm/mmu_notifier.rst
*/
page_remove_rmap(subpage, vma, PageHuge(page));
if (vma->vm_flags & VM_LOCKED)
mlock_page_drain(smp_processor_id());
put_page(page);
}
@ -1930,6 +1932,8 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
* See Documentation/vm/mmu_notifier.rst
*/
page_remove_rmap(subpage, vma, PageHuge(page));
if (vma->vm_flags & VM_LOCKED)
mlock_page_drain(smp_processor_id());
put_page(page);
}