Re: [RFC PATCH 1/3] mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio()

[Shakeel Butt]

On Thu, Jun 11, 2026 at 06:51:22PM +0800, Barry Song (Xiaomi) wrote:
> We always unconditionally drain the LRU before retrying anon folio
> reuse in wp_can_reuse_anon_folio(). Instead, assume !LRU anon folios
> are in lru_cache, and use the refcount to avoid many unnecessary LRU
> drains.
> 
> Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> ---
>  mm/memory.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 56be920c56d7..487a34377a7b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4193,12 +4193,18 @@ static bool wp_can_reuse_anon_folio(struct folio *folio,
>  	 */
>  	if (folio_test_ksm(folio) || folio_ref_count(folio) > 3)
>  		return false;
> -	if (!folio_test_lru(folio))
> +	if (!folio_test_lru(folio)) {
> +		/*
> +		 * Assume folio is on lru_cache and holds a cache reference.
> +		 */
> +		if (folio_ref_count(folio) > 2 + folio_test_swapcache(folio))
> +			return false;

In your experiments, how much amount of drains were reduced due to this specific
check?

I wonder if that data can motivate to introduce lru_add_drain_folio(folio) which
only drains if the given folio is in the local lru_add cache.

>  		/*
>  		 * We cannot easily detect+handle references from
>  		 * remote LRU caches or references to LRU folios.
>  		 */
>  		lru_add_drain();
> +	}
>  	if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio))
>  		return false;
>  	if (!folio_trylock(folio))
> -- 
> 2.39.3 (Apple Git-146)
>