Re: [PATCH -V2 6/7] migrate_pages(): fix failure counting for THP splitting

[Oscar Salvador]

On Mon, Jul 11, 2022 at 04:49:47PM +0800, Huang Ying wrote:
> If THP is failed to be migrated, it may be split and retry.  But after
> splitting, the head page will be left in "from" list, although THP
> migration failure has been counted already.  If the head page is
> failed to be migrated too, the failure will be counted twice
> incorrectly.  So this is fixed in this patch via moving the head page
> of THP after splitting to "thp_split_pages" too.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

> ---
>  mm/migrate.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8cce73b7c046..557708ce13a1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1306,6 +1306,8 @@ static inline int try_split_thp(struct page *page, struct list_head *split_pages
>  	lock_page(page);
>  	rc = split_huge_page_to_list(page, split_pages);
>  	unlock_page(page);
> +	if (!rc)
> +		list_move_tail(&page->lru, split_pages);
>  
>  	return rc;
>  }
> @@ -1365,7 +1367,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  		thp_retry = 0;
>  
>  		list_for_each_entry_safe(page, page2, from, lru) {
> -retry:
>  			/*
>  			 * THP statistics is based on the source huge page.
>  			 * Capture required information that might get lost
> @@ -1412,7 +1413,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  					nr_thp_failed++;
>  					if (!try_split_thp(page, &thp_split_pages)) {
>  						nr_thp_split++;
> -						goto retry;
> +						break;
>  					}
>  				/* Hugetlb migration is unsupported */
>  				} else if (!no_subpage_counting) {
> @@ -1432,7 +1433,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
>  					/* THP NUMA faulting doesn't split THP to retry. */
>  					if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
>  						nr_thp_split++;
> -						goto retry;
> +						break;
>  					}
>  				} else if (!no_subpage_counting) {
>  					nr_failed++;
> -- 
> 2.30.2
> 
> 

-- 
Oscar Salvador
SUSE Labs