Re: [PATCH v2] mm/migrate: make migrate_pages_batch() stats consistent.

[Huang, Ying]

Zi Yan <zi.yan@xxxxxxxx> writes:

> From: Zi Yan <ziy@xxxxxxxxxx>
>
> As Ying pointed out in [1], stats->nr_thp_failed needs to be updated to
> avoid stats inconsistency between MIGRATE_SYNC and MIGRATE_ASYNC when
> calling migrate_pages_batch().
>
> Because if not, when migrate_pages_batch() is called via
> migrate_pages(MIGRATE_ASYNC), nr_thp_failed will not be increased and
> when migrate_pages_batch() is called via migrate_pages(MIGRATE_SYNC*),
> nr_thp_failed will be increase in migrate_pages_sync() by
> stats->nr_thp_failed += astats.nr_thp_split.
>
> [1] https://lore.kernel.org/linux-mm/87msnq7key.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>

LGTM, Thanks!

Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>

> ---
>  mm/migrate.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 66c74b89d3de..781979567f64 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1645,6 +1645,10 @@ static int migrate_pages_batch(struct list_head *from,
>  			 * migrate_pages() may report success with (split but
>  			 * unmigrated) pages still on its fromlist; whereas it
>  			 * always reports success when its fromlist is empty.
> +			 * stats->nr_thp_failed should be increased too,
> +			 * otherwise stats inconsistency will happen when
> +			 * migrate_pages_batch is called via migrate_pages()
> +			 * with MIGRATE_SYNC and MIGRATE_ASYNC.
>  			 *
>  			 * Only check it without removing it from the list.
>  			 * Since the folio can be on deferred_split_scan()
> @@ -1661,6 +1665,7 @@ static int migrate_pages_batch(struct list_head *from,
>  			   !list_empty(&folio->_deferred_list)) {
>  				if (try_split_folio(folio, split_folios) == 0) {
>  					nr_failed++;
> +					stats->nr_thp_failed += is_thp;
>  					stats->nr_thp_split += is_thp;
>  					stats->nr_split++;
>  					continue;
>
> base-commit: 7c4c5a2ebbcea9031dbb130bb529c8eba025b16a