linux-kernel - Re: [PATCH -V2 3/7] migrate_pages(): fix THP failure counting for -ENOMEM

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Date:   Mon, 11 Jul 2022 14:01:55 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH -V2 3/7] migrate_pages(): fix THP failure counting for
 -ENOMEM

On Mon, Jul 11, 2022 at 04:49:44PM +0800, 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 isn't fixed because it's not used.  Added some
> comments for it per Baolin's suggestion.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

> ---
>  mm/migrate.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 794312072eb3..38e2c789a9c3 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1426,11 +1426,11 @@ 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 +1446,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  				 * the caller otherwise the page refcnt will be leaked.
>  				 */
>  				list_splice_init(&thp_split_pages, from);
> +				/* nr_failed isn't updated for not used */
>  				nr_thp_failed += thp_retry;
>  				goto out;
>  			case -EAGAIN:
> -- 
> 2.30.2
> 
> 

-- 
Oscar Salvador
SUSE Labs