Re: [PATCH v3 20/21] mm/slub: remove DEACTIVATE_TO_* stat items

[Suren Baghdasaryan <surenb@google.com>]

On Fri, Jan 16, 2026 at 2:41 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> The cpu slabs and their deactivations were removed, so remove the unused
> stat items. Weirdly enough the values were also used to control
> __add_partial() adding to head or tail of the list, so replace that with
> a new enum add_mode, which is cleaner.
>
> Reviewed-by: Suren Baghdasaryan <surenb@google.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Same question about UAPI breakage, but otherwise LGTM.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

> ---
>  mm/slub.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 7ec7049c0ca5..c12e90cb2fca 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -324,6 +324,11 @@ static void debugfs_slab_add(struct kmem_cache *);
>  static inline void debugfs_slab_add(struct kmem_cache *s) { }
>  #endif
>
> +enum add_mode {
> +       ADD_TO_HEAD,
> +       ADD_TO_TAIL,
> +};
> +
>  enum stat_item {
>         ALLOC_PCS,              /* Allocation from percpu sheaf */
>         ALLOC_FASTPATH,         /* Allocation from cpu slab */
> @@ -343,8 +348,6 @@ enum stat_item {
>         CPUSLAB_FLUSH,          /* Abandoning of the cpu slab */
>         DEACTIVATE_FULL,        /* Cpu slab was full when deactivated */
>         DEACTIVATE_EMPTY,       /* Cpu slab was empty when deactivated */
> -       DEACTIVATE_TO_HEAD,     /* Cpu slab was moved to the head of partials */
> -       DEACTIVATE_TO_TAIL,     /* Cpu slab was moved to the tail of partials */
>         DEACTIVATE_REMOTE_FREES,/* Slab contained remotely freed objects */
>         DEACTIVATE_BYPASS,      /* Implicit deactivation */
>         ORDER_FALLBACK,         /* Number of times fallback was necessary */
> @@ -3268,10 +3271,10 @@ static inline void slab_clear_node_partial(struct slab *slab)
>   * Management of partially allocated slabs.
>   */
>  static inline void
> -__add_partial(struct kmem_cache_node *n, struct slab *slab, int tail)
> +__add_partial(struct kmem_cache_node *n, struct slab *slab, enum add_mode mode)
>  {
>         n->nr_partial++;
> -       if (tail == DEACTIVATE_TO_TAIL)
> +       if (mode == ADD_TO_TAIL)
>                 list_add_tail(&slab->slab_list, &n->partial);
>         else
>                 list_add(&slab->slab_list, &n->partial);
> @@ -3279,10 +3282,10 @@ __add_partial(struct kmem_cache_node *n, struct slab *slab, int tail)
>  }
>
>  static inline void add_partial(struct kmem_cache_node *n,
> -                               struct slab *slab, int tail)
> +                               struct slab *slab, enum add_mode mode)
>  {
>         lockdep_assert_held(&n->list_lock);
> -       __add_partial(n, slab, tail);
> +       __add_partial(n, slab, mode);
>  }
>
>  static inline void remove_partial(struct kmem_cache_node *n,
> @@ -3375,7 +3378,7 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s, struct slab *slab,
>         if (slab->inuse == slab->objects)
>                 add_full(s, n, slab);
>         else
> -               add_partial(n, slab, DEACTIVATE_TO_HEAD);
> +               add_partial(n, slab, ADD_TO_HEAD);
>
>         inc_slabs_node(s, nid, slab->objects);
>         spin_unlock_irqrestore(&n->list_lock, flags);
> @@ -3996,7 +3999,7 @@ static unsigned int alloc_from_new_slab(struct kmem_cache *s, struct slab *slab,
>                         n = get_node(s, slab_nid(slab));
>                         spin_lock_irqsave(&n->list_lock, flags);
>                 }
> -               add_partial(n, slab, DEACTIVATE_TO_HEAD);
> +               add_partial(n, slab, ADD_TO_HEAD);
>                 spin_unlock_irqrestore(&n->list_lock, flags);
>         }
>
> @@ -5064,7 +5067,7 @@ static noinline void free_to_partial_list(
>                         /* was on full list */
>                         remove_full(s, n, slab);
>                         if (!slab_free) {
> -                               add_partial(n, slab, DEACTIVATE_TO_TAIL);
> +                               add_partial(n, slab, ADD_TO_TAIL);
>                                 stat(s, FREE_ADD_PARTIAL);
>                         }
>                 } else if (slab_free) {
> @@ -5184,7 +5187,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>          * then add it.
>          */
>         if (unlikely(was_full)) {
> -               add_partial(n, slab, DEACTIVATE_TO_TAIL);
> +               add_partial(n, slab, ADD_TO_TAIL);
>                 stat(s, FREE_ADD_PARTIAL);
>         }
>         spin_unlock_irqrestore(&n->list_lock, flags);
> @@ -6564,7 +6567,7 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi
>                                 continue;
>
>                         list_del(&slab->slab_list);
> -                       add_partial(n, slab, DEACTIVATE_TO_HEAD);
> +                       add_partial(n, slab, ADD_TO_HEAD);
>                 }
>
>                 spin_unlock_irqrestore(&n->list_lock, flags);
> @@ -7031,7 +7034,7 @@ static void early_kmem_cache_node_alloc(int node)
>          * No locks need to be taken here as it has just been
>          * initialized and there is no concurrent access.
>          */
> -       __add_partial(n, slab, DEACTIVATE_TO_HEAD);
> +       __add_partial(n, slab, ADD_TO_HEAD);
>  }
>
>  static void free_kmem_cache_nodes(struct kmem_cache *s)
> @@ -8719,8 +8722,6 @@ STAT_ATTR(FREE_SLAB, free_slab);
>  STAT_ATTR(CPUSLAB_FLUSH, cpuslab_flush);
>  STAT_ATTR(DEACTIVATE_FULL, deactivate_full);
>  STAT_ATTR(DEACTIVATE_EMPTY, deactivate_empty);
> -STAT_ATTR(DEACTIVATE_TO_HEAD, deactivate_to_head);
> -STAT_ATTR(DEACTIVATE_TO_TAIL, deactivate_to_tail);
>  STAT_ATTR(DEACTIVATE_REMOTE_FREES, deactivate_remote_frees);
>  STAT_ATTR(DEACTIVATE_BYPASS, deactivate_bypass);
>  STAT_ATTR(ORDER_FALLBACK, order_fallback);
> @@ -8823,8 +8824,6 @@ static struct attribute *slab_attrs[] = {
>         &cpuslab_flush_attr.attr,
>         &deactivate_full_attr.attr,
>         &deactivate_empty_attr.attr,
> -       &deactivate_to_head_attr.attr,
> -       &deactivate_to_tail_attr.attr,
>         &deactivate_remote_frees_attr.attr,
>         &deactivate_bypass_attr.attr,
>         &order_fallback_attr.attr,
>
> --
> 2.52.0
>