Re: [RFC PATCH v5 02/14] mm/mglru: extract lruvec_populated_min_seq() helper

[KunWu Chan]

On Fri, Oct 23, 2026 at 6:02 AM Barry Song (Xiaomi) <baohua@xxxxxxxxxx> wrote:
>
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> The search for the oldest populated generation of a type, previously
> embedded in try_to_inc_min_seq(), is extracted into the new
> lruvec_populated_min_seq() helper. It returns the oldest populated seq
> of a given type, bounded by the given max_seq so the search never goes
> beyond it.
>
> No functional change.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> Signed-off-by: Barry Song (Xiaomi) <baohua@xxxxxxxxxx>
> ---
>  mm/vmscan.c | 43 +++++++++++++++++++++++++++++--------------
>  1 file changed, 29 insertions(+), 14 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3be0d6c04a82..500ef23949fd 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4131,30 +4131,45 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, int swappiness)
>         return true;
>  }
>
> +/* Similar to lruvec_evictable_size, return the oldest populated seq of the type */
> +static unsigned long lruvec_populated_min_seq(struct lruvec *lruvec, int type,
> +                                             unsigned long max_seq)
> +{
> +       int gen, zone;
> +       unsigned long min_seq;
> +       struct lru_gen_folio *lrugen = &lruvec->lrugen;
> +
> +       lockdep_assert_held(&lruvec->lru_lock);
> +
> +       min_seq = READ_ONCE(lrugen->min_seq[type]);
> +       while (min_seq <= max_seq) {
> +               gen = lru_gen_from_seq(min_seq);
> +               for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> +                       if (!list_empty(&lrugen->folios[gen][type][zone]))
> +                               return min_seq;
> +               }
> +               min_seq++;
> +       }
> +
> +       return max_seq;
> +}
> +
>  static void try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
>  {
> -       int gen, type, zone;
> +       int type;
>         bool seq_inc_flag = false;
>         struct lru_gen_folio *lrugen = &lruvec->lrugen;
>         DEFINE_MIN_SEQ(lruvec);
> +       unsigned long seq;
>
>         VM_WARN_ON_ONCE(!seq_is_valid(lruvec));
>
> -       /* find the oldest populated generation */
> +       /* Requires at least MIN_NR_GENS gens for basic functionality */
> +       seq = lrugen->max_seq - MIN_NR_GENS;
>         for_each_evictable_type(type, swappiness) {
> -               while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
> -                       gen = lru_gen_from_seq(min_seq[type]);
> -
> -                       for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> -                               if (!list_empty(&lrugen->folios[gen][type][zone]))
> -                                       goto next;
> -                       }
> -
> -                       min_seq[type]++;
> +               min_seq[type] = lruvec_populated_min_seq(lruvec, type, seq + 1);
> +               if (min_seq[type] > lrugen->min_seq[type])
>                         seq_inc_flag = true;
> -               }
> -next:
> -               ;
>         }
>
>         /*
> --
> 2.34.1
>

The helper preserves the original search result, including the
terminal sequence when no populated generation is found.

Reviewed-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>

Thanks,
Kunwu