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From:   Yu Zhao <yuzhao@google.com>
Date:   Fri, 18 Mar 2022 21:11:09 -0600
Message-ID: <CAOUHufbiSShp=khZFL6BmJKNNkG-LBrsPoLwYxewcgtZhi5tFg@mail.gmail.com>
Subject: Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation
To:     Barry Song <21cnbao@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
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On Fri, Mar 18, 2022 at 9:01 PM Barry Song <21cnbao@gmail.com> wrote:
>
> > +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
> > +{
> > +       unsigned long old_flags, new_flags;
> > +       int type = folio_is_file_lru(folio);
> > +       struct lru_gen_struct *lrugen = &lruvec->lrugen;
> > +       int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
> > +
> > +       do {
> > +               new_flags = old_flags = READ_ONCE(folio->flags);
> > +               VM_BUG_ON_FOLIO(!(new_flags & LRU_GEN_MASK), folio);
> > +
> > +               new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
> > +               new_gen = (old_gen + 1) % MAX_NR_GENS;
>
> new_gen is assigned twice, i assume you mean
>                old_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
>                new_gen = (old_gen + 1) % MAX_NR_GENS;
>
> or do you always mean new_gen =  lru_gen_from_seq(min_seq) + 1?

Thanks a lot for your attention to details!

The first line should be in the next patch but I overlooked during the
last refactoring:

  new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+ /* folio_update_gen() has promoted this page? */
+ if (new_gen >= 0 && new_gen != old_gen)
+ return new_gen;
+
  new_gen = (old_gen + 1) % MAX_NR_GENS;