Re: [PATCH v4 10/11] mm: lru: add VM_BUG_ON_FOLIO to lru maintenance function

[Roman Gushchin]

On Tue, May 24, 2022 at 02:05:50PM +0800, Muchun Song wrote:
> We need to make sure that the page is deleted from or added to the
> correct lruvec list. So add a VM_BUG_ON_FOLIO() to catch invalid
> users.
> 
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  include/linux/mm_inline.h | 6 ++++++
>  mm/vmscan.c               | 1 -
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index ac32125745ab..30d2393da613 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -97,6 +97,8 @@ void lruvec_add_folio(struct lruvec *lruvec, struct folio *folio)
>  {
>  	enum lru_list lru = folio_lru_list(folio);
>  
> +	VM_BUG_ON_FOLIO(!folio_matches_lruvec(folio, lruvec), folio);
> +
>  	update_lru_size(lruvec, lru, folio_zonenum(folio),
>  			folio_nr_pages(folio));
>  	if (lru != LRU_UNEVICTABLE)
> @@ -114,6 +116,8 @@ void lruvec_add_folio_tail(struct lruvec *lruvec, struct folio *folio)
>  {
>  	enum lru_list lru = folio_lru_list(folio);
>  
> +	VM_BUG_ON_FOLIO(!folio_matches_lruvec(folio, lruvec), folio);
> +
>  	update_lru_size(lruvec, lru, folio_zonenum(folio),
>  			folio_nr_pages(folio));
>  	/* This is not expected to be used on LRU_UNEVICTABLE */
> @@ -131,6 +135,8 @@ void lruvec_del_folio(struct lruvec *lruvec, struct folio *folio)
>  {
>  	enum lru_list lru = folio_lru_list(folio);
>  
> +	VM_BUG_ON_FOLIO(!folio_matches_lruvec(folio, lruvec), folio);
> +
>  	if (lru != LRU_UNEVICTABLE)
>  		list_del(&folio->lru);
>  	update_lru_size(lruvec, lru, folio_zonenum(folio),
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 761d5e0dd78d..6c9e2eafc8f9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2281,7 +2281,6 @@ static unsigned int move_pages_to_lru(struct list_head *list)
>  			continue;
>  		}
>  
> -		VM_BUG_ON_PAGE(!folio_matches_lruvec(folio, lruvec), page);

The commit log describes well why we need to add new BUG_ON's. Please, add
something on why this is removed.


Thanks!