Re: [PATCH] migrate_pages_batch: fix statistics for longterm pin retry

[Baolin Wang]

On 4/17/2023 7:59 AM, Huang Ying wrote:
> In commit fd4a7ac32918 ("mm: migrate: try again if THP split is failed
> due to page refcnt"), if the THP splitting fails due to page reference
> count, we will retry to improve migration successful rate.  But the
> failed splitting is counted as migration failure and migration retry,
> which will cause duplicated failure counting.  So, in this patch, this
> is fixed via undoing the failure counting if we decide to retry.  The
> patch is tested via failure injection.

Makes sense to me. Thanks.
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

> Fixes: fd4a7ac32918 ("mm: migrate: try again if THP split is failed due to page refcnt")
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: Alistair Popple <apopple@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> ---
>   mm/migrate.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index b34a0f383795..47a1e8445f45 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1743,6 +1743,9 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
>   							large_retry++;
>   							thp_retry += is_thp;
>   							nr_retry_pages += nr_pages;
> +							/* Undo duplicated failure counting. */
> +							nr_large_failed--;
> +							stats->nr_thp_failed -= is_thp;
>   							break;
>   						}
>   					}