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Message-ID: <CAOUHufYz+FmxQ8yoocbV8LP05HGU=cRoqJE1-bQa0KyLofJYhQ@mail.gmail.com>
Date: Wed, 25 Jan 2023 14:13:00 -0700
From: Yu Zhao <yuzhao@...gle.com>
To: Nhat Pham <nphamcs@...il.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 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.
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