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>
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);
* 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);
}
* 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);
}