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Date: Thu, 26 Jan 2023 09:08:32 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Yu Zhao <yuzhao@...gle.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, bfoster@...hat.com,
willy@...radead.org, linux-api@...r.kernel.org,
kernel-team@...a.com
Subject: Re: [PATCH v7 1/3] workingset: refactor LRU refault to expose refault
recency check
On Wed, Jan 25, 2023 at 1:13 PM Yu Zhao <yuzhao@...gle.com> wrote:
>
> On Mon, Jan 23, 2023 at 7:11 PM Nhat Pham <nphamcs@...il.com> 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@...il.com>
> > ---
> > 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...
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