linux-kernel - Re: [PATCH v2 2/4] workingset: refactor LRU refault to expose refault recency check

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Date:   Mon, 5 Dec 2022 16:49:00 -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, kernel-team@...a.com
Subject: Re: [PATCH v2 2/4] workingset: refactor LRU refault to expose refault
 recency check

On Mon, Dec 5, 2022 at 10:51 AM 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      | 143 +++++++++++++++++++++++++++++--------------
>  2 files changed, 99 insertions(+), 45 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..44b331ce3040 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)));
> +}

Nit: not refactoring actually looks cleaner to me -- there are only a
few lines of duplicated code and you can get rid of 4 parameters
including the unused workingset in the next patch.