Re: [PATCH 2/6] mm/mglru: batch update lrugen->protected in inc_min_seq()

[Baoquan He <baoquan.he@linux.dev>]

On 08/21/26 at 06:25pm, Barry Song (Xiaomi) wrote:
> Avoid updating lrugen->protected with WRITE_ONCE() for each folio,
> which may prevent potential compiler optimizations. Accumulate the
> updates locally and apply them in a batch instead.

Wondering how much efficiency this can bring, is there a number for this
standalone patch?

> 
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
> ---
>  mm/vmscan.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0d74fc00abd3..99ee3c833d54 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3931,7 +3931,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  	/* prevent cold/hot inversion if the type is evictable */
>  	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
>  		struct list_head *head = &lrugen->folios[old_gen][type][zone];
> -		unsigned long delta = 0;
> +		unsigned long protected[MAX_NR_TIERS] = {}, delta = 0;
>  
>  		while (!list_empty(head)) {
>  			struct folio *folio = lru_to_folio(head);
> @@ -3953,8 +3953,7 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  			if (refs + workingset != BIT(LRU_REFS_WIDTH) + 1) {
>  				int tier = lru_tier_from_refs(refs, workingset);
>  
> -				WRITE_ONCE(lrugen->protected[hist][type][tier],
> -					   lrugen->protected[hist][type][tier] + nr_pages);
> +				protected[tier] += nr_pages;
>  			}
>  
>  			if (!--remaining)
> @@ -3964,6 +3963,9 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>  			   lrugen->nr_pages[old_gen][type][zone] - delta);
>  		WRITE_ONCE(lrugen->nr_pages[target_gen][type][zone],
>  			   lrugen->nr_pages[target_gen][type][zone] + delta);
> +		for (int tier = 0; tier < MAX_NR_TIERS; tier++)
> +			WRITE_ONCE(lrugen->protected[hist][type][tier],
> +				   lrugen->protected[hist][type][tier] + protected[tier]);
>  		if (!remaining)
>  			return false;
>  	}
> -- 
> 2.34.1
>