Re: [PATCH 5/6] mm/mglru: move folios from oldest gen to second-oldest gen from head to tail

[Baoquan He]

On 08/21/26 at 06:25pm, Barry Song (Xiaomi) wrote:
> For reclamation, it makes sense to reclaim folios from tail to
> head, as folios near the head are relatively hot. However, when
> moving folios from the oldest generation to the second-oldest
> generation, using the tail-to-head order would effectively cause
> a cold/hot inversion.

This is great, do we need do the similar thing on scan_folios()?
While it's not relevant to this patch.

Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>

> 
> Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> ---
>  mm/vmscan.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7bd01875fade..2fd82b2ca4d1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -191,8 +191,20 @@ struct scan_control {
>  			prefetchw(&prev->_field);			\
>  		}							\
>  	} while (0)
> +#define prefetchw_next_lru_folio(_folio, _base, _field)			\
> +	do {								\
> +		if ((_folio)->lru.next != _base) {			\
> +			struct folio *next;				\
> +									\
> +			next = list_entry((_folio)->lru.next,		\
> +					struct folio, lru);		\
> +			prefetchw(&next->_field);			\
> +		}							\
> +	} while (0)
> +
>  #else
>  #define prefetchw_prev_lru_folio(_folio, _base, _field) do { } while (0)
> +#define prefetchw_next_lru_folio(_folio, _base, _field) do { } while (0)
>  #endif
>  
>  /*
> @@ -3932,9 +3944,10 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
>  		struct list_head *head = &lrugen->folios[old_gen][type][zone];
>  		unsigned long protected[MAX_NR_TIERS] = {}, delta = 0;
> +		struct list_head *pos = head->next;
>  
> -		while (!list_empty(head)) {
> -			struct folio *folio = lru_to_folio(head);
> +		while (pos != head) {
> +			struct folio *folio = list_entry(pos, struct folio, lru);
>  			long nr_pages = folio_nr_pages(folio);
>  			int refs = folio_lru_refs(folio);
>  			bool workingset = folio_test_workingset(folio);
> @@ -3945,6 +3958,8 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  			VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
>  			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
>  
> +			prefetchw_next_lru_folio(folio, head, flags);
> +			pos = pos->next;
>  			new_gen = __folio_inc_gen(folio, old_gen, &gen_increased);
>  			if (gen_increased) {
>  				delta += nr_pages;
> -- 
> 2.34.1
>