Re: [PATCH v2 1/4] mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/24/26 01:16, 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.
> 
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Reviewed-by: Baoquan He <baoquan.he@linux.dev>
> Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
> ---
>  mm/memory.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index ff338c2abe92..f6848f4234a6 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;

I'm not keen on making this function even uglier, so no, not like that.

We have the earlier "folio_ref_count(folio) > 3" check.

In which scenarios can you trigger this such that we would care?

If the answer is "I don't know" there is no reason for a change.

-- 
Cheers,

David