Re: [PATCH v3 1/2] mm/migrate: correct nr_failed in migrate_pages_sync()

[Baolin Wang]

On 10/18/2023 12:31 AM, Zi Yan wrote:
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> nr_failed was missing the large folio splits from migrate_pages_batch()
> and can cause a mismatch between migrate_pages() return value and the
> number of not migrated pages, i.e., when the return value of
> migrate_pages() is 0, there are still pages left in the from page list.
> It will happen when a non-PMD THP large folio fails to migrate due to
> -ENOMEM and is split successfully but not all the split pages are not
> migrated, migrate_pages_batch() would return non-zero, but
> astats.nr_thp_split = 0. nr_failed would be 0 and returned to the caller
> of migrate_pages(), but the not migrated pages are left in the from page
> list without being added back to LRU lists.
>
> Fix it by adding a new nr_split counter for large folio splits and adding
> it to nr_failed in migrate_page_sync() after migrate_pages_batch() is
> done.
>
> Fixes: 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously firstly")
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> ---

LGTM. Feel free to add:
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>