Re: [PATCH 1/8] mm/mglru: consolidate common code for retrieving evitable size

[Axel Rasmussen]

For what it's worth, I applied the full series and ran it through some
basic functional testing, I didn't see any bugs or regressions from
that.

Unfortunately, the best signal would be actually deploying it under
some real serving workloads, but the latency for me to do that + get
results is like order(weeks) and I suspect you don't want to wait that
long. :)

This particular commit looks good besides one minor nitpick:

Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>

On Wed, Mar 18, 2026 at 7:19 PM Chen Ridong <chenridong@xxxxxxxxxxxxxxx> wrote:
>
>
>
> On 2026/3/18 3:08, Kairui Song via B4 Relay wrote:
> > From: Kairui Song <kasong@xxxxxxxxxxx>
> >
> > Merge commonly used code for counting evictable folios in a lruvec.
> >
> > No behavior change.
> >
> > Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
>
> Reviewed-by: Chen Ridong <chenridong@xxxxxxxxxxxxxxx>
>
> > ---
> >  mm/vmscan.c | 42 +++++++++++++++++-------------------------
> >  1 file changed, 17 insertions(+), 25 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 33287ba4a500..d7fc7f1fe06d 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4078,27 +4078,33 @@ static void set_initial_priority(struct pglist_data *pgdat, struct scan_control
> >       sc->priority = clamp(priority, DEF_PRIORITY / 2, DEF_PRIORITY);
> >  }
> >
> > -static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
> > +static long lruvec_evictable_size(struct lruvec *lruvec, int swappiness)
> >  {

Since `total` is unsigned long, should this function likewise return
`unsigned long`? It seems ideal to avoid conversions unless there's a
good reason to do so.

> >       int gen, type, zone;
> > -     unsigned long total = 0;
> > -     int swappiness = get_swappiness(lruvec, sc);
> > +     unsigned long seq, total = 0;
> >       struct lru_gen_folio *lrugen = &lruvec->lrugen;
> > -     struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> >       DEFINE_MAX_SEQ(lruvec);
> >       DEFINE_MIN_SEQ(lruvec);
> >
> >       for_each_evictable_type(type, swappiness) {
> > -             unsigned long seq;
> > -
> >               for (seq = min_seq[type]; seq <= max_seq; seq++) {
> >                       gen = lru_gen_from_seq(seq);
> > -
> >                       for (zone = 0; zone < MAX_NR_ZONES; zone++)
> >                               total += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
> >               }
> >       }
> >
> > +     return total;
> > +}
> > +
> > +static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
> > +{
> > +     unsigned long total;
> > +     int swappiness = get_swappiness(lruvec, sc);
> > +     struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> > +
> > +     total = lruvec_evictable_size(lruvec, swappiness);
> > +
> >       /* whether the size is big enough to be helpful */
> >       return mem_cgroup_online(memcg) ? (total >> sc->priority) : total;
> >  }
> > @@ -4921,9 +4927,6 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
> >  static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
> >                            int swappiness, unsigned long *nr_to_scan)
> >  {
> > -     int gen, type, zone;
> > -     unsigned long size = 0;
> > -     struct lru_gen_folio *lrugen = &lruvec->lrugen;
> >       DEFINE_MIN_SEQ(lruvec);
> >
> >       *nr_to_scan = 0;
> > @@ -4931,18 +4934,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
> >       if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
> >               return true;
> >
> > -     for_each_evictable_type(type, swappiness) {
> > -             unsigned long seq;
> > -
> > -             for (seq = min_seq[type]; seq <= max_seq; seq++) {
> > -                     gen = lru_gen_from_seq(seq);
> > -
> > -                     for (zone = 0; zone < MAX_NR_ZONES; zone++)
> > -                             size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L);
> > -             }
> > -     }
> > -
> > -     *nr_to_scan = size;
> > +     *nr_to_scan = lruvec_evictable_size(lruvec, swappiness);
> >       /* better to run aging even though eviction is still possible */
> >       return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq;
> >  }
> > @@ -4954,7 +4946,7 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
> >   */
> >  static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
> >  {
> > -     bool success;
> > +     bool need_aging;
>
> I have suffered a lot because of this name. Thank you.
>
> >       unsigned long nr_to_scan;
> >       struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> >       DEFINE_MAX_SEQ(lruvec);
> > @@ -4962,7 +4954,7 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int s
> >       if (mem_cgroup_below_min(sc->target_mem_cgroup, memcg))
> >               return -1;
> >
> > -     success = should_run_aging(lruvec, max_seq, swappiness, &nr_to_scan);
> > +     need_aging = should_run_aging(lruvec, max_seq, swappiness, &nr_to_scan);
> >
> >       /* try to scrape all its memory if this memcg was deleted */
> >       if (nr_to_scan && !mem_cgroup_online(memcg))
> > @@ -4971,7 +4963,7 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int s
> >       nr_to_scan = apply_proportional_protection(memcg, sc, nr_to_scan);
> >
> >       /* try to get away with not aging at the default priority */
> > -     if (!success || sc->priority == DEF_PRIORITY)
> > +     if (!need_aging || sc->priority == DEF_PRIORITY)
> >               return nr_to_scan >> sc->priority;
> >
> >       /* stop scanning this lruvec as it's low on cold folios */
> >
>
> --
> Best regards,
> Ridong
>