linux-kernel - Re: [PATCH v5 3/9] slub: Keep track of whether slub is on the per-node partial list

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Date:   Wed, 22 Nov 2023 10:21:07 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     chengming.zhou@...ux.dev
Cc:     vbabka@...e.cz, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, roman.gushchin@...ux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v5 3/9] slub: Keep track of whether slub is on the
 per-node partial list

On Thu, Nov 2, 2023 at 12:24 PM <chengming.zhou@...ux.dev> wrote:
>
> From: Chengming Zhou <zhouchengming@...edance.com>
>
> Now we rely on the "frozen" bit to see if we should manipulate the
> slab->slab_list, which will be changed in the following patch.
>
> Instead we introduce another way to keep track of whether slub is on
> the per-node partial list, here we reuse the PG_workingset bit.
>
> We use __set_bit and __clear_bit directly instead of the atomic version
> for better performance and it's safe since it's protected by the slub
> node list_lock.
>
> Suggested-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> Tested-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> ---
>  mm/slub.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 03384cd965c5..eed8ae0dbaf9 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2116,6 +2116,25 @@ static void discard_slab(struct kmem_cache *s, struct slab *slab)
>         free_slab(s, slab);
>  }
>
> +/*
> + * SLUB reuses PG_workingset bit to keep track of whether it's on
> + * the per-node partial list.
> + */
> +static inline bool slab_test_node_partial(const struct slab *slab)
> +{
> +       return folio_test_workingset((struct folio *)slab_folio(slab));
> +}
> +
> +static inline void slab_set_node_partial(struct slab *slab)
> +{
> +       __set_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
> +}
> +
> +static inline void slab_clear_node_partial(struct slab *slab)
> +{
> +       __clear_bit(PG_workingset, folio_flags(slab_folio(slab), 0));
> +}
> +
>  /*
>   * Management of partially allocated slabs.
>   */
> @@ -2127,6 +2146,7 @@ __add_partial(struct kmem_cache_node *n, struct slab *slab, int tail)
>                 list_add_tail(&slab->slab_list, &n->partial);
>         else
>                 list_add(&slab->slab_list, &n->partial);
> +       slab_set_node_partial(slab);
>  }
>
>  static inline void add_partial(struct kmem_cache_node *n,
> @@ -2141,6 +2161,7 @@ static inline void remove_partial(struct kmem_cache_node *n,
>  {
>         lockdep_assert_held(&n->list_lock);
>         list_del(&slab->slab_list);
> +       slab_clear_node_partial(slab);
>         n->nr_partial--;
>  }
>
> @@ -4833,6 +4854,7 @@ static int __kmem_cache_do_shrink(struct kmem_cache *s)
>
>                         if (free == slab->objects) {
>                                 list_move(&slab->slab_list, &discard);
> +                               slab_clear_node_partial(slab);
>                                 n->nr_partial--;
>                                 dec_slabs_node(s, node, slab->objects);
>                         } else if (free <= SHRINK_PROMOTE_MAX)
> --

Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>