Re: [PATCH v3 6/7] mm/mglru: move folios from oldest gen to second-oldest gen from head to tail

[Baolin Wang]

On 9/2/26 7:24 AM, 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.
>
> Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>
> Tested-by: Xueyuan Chen <xueyuan.chen21@xxxxxxxxx>
> Reviewed-by: Lian Wang <lianux.mm@xxxxxxxxx>
> ---
>   mm/vmscan.c | 23 +++++++++++++++++++++--
>   1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1907a946840d..76dfa9575852 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -192,11 +192,27 @@ static inline void prefetchw_prev_lru_folio(struct folio *folio,
>   		prefetchw(&prev->flags);
>   	}
>   }
> +
> +static inline void prefetchw_next_lru_folio(struct folio *folio,
> +		struct list_head *base)
> +{
> +	if (folio->lru.next != base) {
> +		struct folio *next;
> +
> +		next = list_entry(folio->lru.next, struct folio, lru);
> +		prefetchw(&next->flags);
> +	}
> +}

You did not mention in the commit message why this prefetch was added. 
Just curious, does it really help performance?