Re: [PATCH v7 1/3] workingset: refactor LRU refault to expose refault recency check

[Nhat Pham]

On Wed, Jan 25, 2023 at 1:13 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote:
>
> On Mon, Jan 23, 2023 at 7:11 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
> >
> > In preparation for computing recently evicted pages in cachestat,
> > refactor workingset_refault and lru_gen_refault to expose a helper
> > function that would test if an evicted page is recently evicted.
> >
> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
> > ---
> >  include/linux/swap.h |   1 +
> >  mm/workingset.c      | 142 +++++++++++++++++++++++++++++--------------
> >  2 files changed, 97 insertions(+), 46 deletions(-)
> >
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index a18cf4b7c724..dae6f6f955eb 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -361,6 +361,7 @@ static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
> >  }
> >
> >  /* linux/mm/workingset.c */
> > +bool workingset_test_recent(void *shadow, bool file, bool *workingset);
> >  void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
> >  void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg);
> >  void workingset_refault(struct folio *folio, void *shadow);
> > diff --git a/mm/workingset.c b/mm/workingset.c
> > index 79585d55c45d..2f2d94867366 100644
> > --- a/mm/workingset.c
> > +++ b/mm/workingset.c
> > @@ -244,6 +244,30 @@ static void *lru_gen_eviction(struct folio *folio)
> >         return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
> >  }
> >
> > +/*
> > + * Test if the folio is recently evicted.
> > + *
> > + * As a side effect, also populates the references with
> > + * values unpacked from the shadow of the evicted folio.
> > + */
> > +static bool lru_gen_test_recent(void *shadow, bool file, int *memcgid,
> > +               struct pglist_data **pgdat, unsigned long *token, bool *workingset)
> > +{
> > +       struct mem_cgroup *eviction_memcg;
> > +       struct lruvec *lruvec;
> > +       struct lru_gen_struct *lrugen;
> > +       unsigned long min_seq;
> > +
> > +       unpack_shadow(shadow, memcgid, pgdat, token, workingset);
> > +       eviction_memcg = mem_cgroup_from_id(*memcgid);
> > +
> > +       lruvec = mem_cgroup_lruvec(eviction_memcg, *pgdat);
> > +       lrugen = &lruvec->lrugen;
> > +
> > +       min_seq = READ_ONCE(lrugen->min_seq[file]);
> > +       return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH));
> > +}
> > +
> >  static void lru_gen_refault(struct folio *folio, void *shadow)
> >  {
> >         int hist, tier, refs;
> > @@ -258,23 +282,22 @@ static void lru_gen_refault(struct folio *folio, void *shadow)
> >         int type = folio_is_file_lru(folio);
> >         int delta = folio_nr_pages(folio);
> >
> > -       unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset);
> > -
> > -       if (pgdat != folio_pgdat(folio))
> > -               return;
> > -
> >         rcu_read_lock();
> >
> > +       if (!lru_gen_test_recent(shadow, type, &memcg_id, &pgdat, &token,
> > +                       &workingset))
> > +               goto unlock;
> > +
> >         memcg = folio_memcg_rcu(folio);
> >         if (memcg_id != mem_cgroup_id(memcg))
> >                 goto unlock;
> >
> > +       if (pgdat != folio_pgdat(folio))
> > +               return;
> > +
> >         lruvec = mem_cgroup_lruvec(memcg, pgdat);
> >         lrugen = &lruvec->lrugen;
> > -
> >         min_seq = READ_ONCE(lrugen->min_seq[type]);
> > -       if ((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)))
> > -               goto unlock;
> >
> >         hist = lru_hist_from_seq(min_seq);
> >         /* see the comment in folio_lru_refs() */
> > @@ -306,6 +329,12 @@ static void *lru_gen_eviction(struct folio *folio)
> >         return NULL;
> >  }
> >
> > +static bool lru_gen_test_recent(void *shadow, bool file, int *memcgid,
> > +               struct pglist_data **pgdat, unsigned long *token, bool *workingset)
> > +{
> > +       return false;
> > +}
> > +
> >  static void lru_gen_refault(struct folio *folio, void *shadow)
> >  {
> >  }
> > @@ -373,40 +402,31 @@ void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
> >                                 folio_test_workingset(folio));
> >  }
> >
> > -/**
> > - * workingset_refault - Evaluate the refault of a previously evicted folio.
> > - * @folio: The freshly allocated replacement folio.
> > - * @shadow: Shadow entry of the evicted folio.
> > +/*
> > + * Test if the folio is recently evicted by checking if
> > + * refault distance of shadow exceeds workingset size.
> >   *
> > - * Calculates and evaluates the refault distance of the previously
> > - * evicted folio in the context of the node and the memcg whose memory
> > - * pressure caused the eviction.
> > + * As a side effect, populate workingset with the value
> > + * unpacked from shadow.
> >   */
> > -void workingset_refault(struct folio *folio, void *shadow)
> > +bool workingset_test_recent(void *shadow, bool file, bool *workingset)
> >  {
> > -       bool file = folio_is_file_lru(folio);
> >         struct mem_cgroup *eviction_memcg;
> >         struct lruvec *eviction_lruvec;
> >         unsigned long refault_distance;
> >         unsigned long workingset_size;
> > -       struct pglist_data *pgdat;
> > -       struct mem_cgroup *memcg;
> > -       unsigned long eviction;
> > -       struct lruvec *lruvec;
> >         unsigned long refault;
> > -       bool workingset;
> >         int memcgid;
> > -       long nr;
> > +       struct pglist_data *pgdat;
> > +       unsigned long eviction;
> >
> > -       if (lru_gen_enabled()) {
> > -               lru_gen_refault(folio, shadow);
> > -               return;
> > -       }
> > +       if (lru_gen_enabled())
> > +               lru_gen_test_recent(shadow, file, &memcgid, &pgdat, &eviction,
> > +                       workingset);
>
> Missing "return", which was correctly handled in your v2, btw.

Oops copy-paste hazard. I'll fix this...