Re: [PATCH 3/7] migrate_pages(): fix THP failure counting for -ENOMEM

[Baolin Wang]

On 6/24/2022 10:53 AM, Huang Ying wrote:
> In unmap_and_move(), if the new THP cannot be allocated, -ENOMEM will
> be returned, and migrate_pages() will try to split the THP unless
> "reason" is MR_NUMA_MISPLACED (that is, nosplit == true).  But when
> nosplit == true, the THP migration failure will not be counted.  This
> is incorrect.  So in this patch, the THP migration failure will be
> counted for -ENOMEM regardless of nosplit is true or false.  The
> nr_failed counting is fixed too, although that is not used actually.

No strong opinion about the 'nr_failed' updating, like you said, we did 
not use it in this case. Maybe just add some comments instead of adding 
some unused code? Otherwise looks good to me.

Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> --- >   mm/migrate.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 82444e7df9f1..542533e4e3cf 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1425,11 +1425,11 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>   				/*
>   				 * When memory is low, don't bother to try to migrate
>   				 * other pages, just exit.
> -				 * THP NUMA faulting doesn't split THP to retry.
>   				 */
> -				if (is_thp && !nosplit) {
> +				if (is_thp) {
>   					nr_thp_failed++;
> -					if (!try_split_thp(page, &thp_split_pages)) {
> +					/* THP NUMA faulting doesn't split THP to retry. */
> +					if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
>   						nr_thp_split++;
>   						goto retry;
>   					}
> @@ -1446,6 +1446,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>   				 */
>   				list_splice_init(&thp_split_pages, from);
>   				nr_thp_failed += thp_retry;
> +				if (!no_subpage_counting)
> +					nr_failed += retry;
>   				goto out;
>   			case -EAGAIN:
>   				if (is_thp)