Re: [PATCH v3 19/21] slab: remove frozen slab checks from __slab_free()

[Suren Baghdasaryan]

On Fri, Jan 16, 2026 at 2:41 PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> Currently slabs are only frozen after consistency checks failed. This
> can happen only in caches with debugging enabled, and those use
> free_to_partial_list() for freeing. The non-debug operation of
> __slab_free() can thus stop considering the frozen field, and we can
> remove the FREE_FROZEN stat.
>
> Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Functionally looks fine to me. Do we need to do something about the
UAPI breakage that removal of a sysfs node might cause?

Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

> ---
>  mm/slub.c | 22 ++++------------------
>  1 file changed, 4 insertions(+), 18 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 476a279f1a94..7ec7049c0ca5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -333,7 +333,6 @@ enum stat_item {
>         FREE_RCU_SHEAF_FAIL,    /* Failed to free to a rcu_free sheaf */
>         FREE_FASTPATH,          /* Free to cpu slab */
>         FREE_SLOWPATH,          /* Freeing not to cpu slab */
> -       FREE_FROZEN,            /* Freeing to frozen slab */
>         FREE_ADD_PARTIAL,       /* Freeing moves slab to partial list */
>         FREE_REMOVE_PARTIAL,    /* Freeing removes last object */
>         ALLOC_FROM_PARTIAL,     /* Cpu slab acquired from node partial list */
> @@ -5103,7 +5102,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>                         unsigned long addr)
>
>  {
> -       bool was_frozen, was_full;
> +       bool was_full;
>         struct freelist_counters old, new;
>         struct kmem_cache_node *n = NULL;
>         unsigned long flags;
> @@ -5126,7 +5125,6 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>                 old.counters = slab->counters;
>
>                 was_full = (old.freelist == NULL);
> -               was_frozen = old.frozen;
>
>                 set_freepointer(s, tail, old.freelist);
>
> @@ -5139,7 +5137,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>                  * to (due to not being full anymore) the partial list.
>                  * Unless it's frozen.
>                  */
> -               if ((!new.inuse || was_full) && !was_frozen) {
> +               if (!new.inuse || was_full) {
>
>                         n = get_node(s, slab_nid(slab));
>                         /*
> @@ -5158,20 +5156,10 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>         } while (!slab_update_freelist(s, slab, &old, &new, "__slab_free"));
>
>         if (likely(!n)) {
> -
> -               if (likely(was_frozen)) {
> -                       /*
> -                        * The list lock was not taken therefore no list
> -                        * activity can be necessary.
> -                        */
> -                       stat(s, FREE_FROZEN);
> -               }
> -
>                 /*
> -                * In other cases we didn't take the list_lock because the slab
> -                * was already on the partial list and will remain there.
> +                * We didn't take the list_lock because the slab was already on
> +                * the partial list and will remain there.
>                  */
> -
>                 return;
>         }
>
> @@ -8721,7 +8709,6 @@ STAT_ATTR(FREE_RCU_SHEAF, free_rcu_sheaf);
>  STAT_ATTR(FREE_RCU_SHEAF_FAIL, free_rcu_sheaf_fail);
>  STAT_ATTR(FREE_FASTPATH, free_fastpath);
>  STAT_ATTR(FREE_SLOWPATH, free_slowpath);
> -STAT_ATTR(FREE_FROZEN, free_frozen);
>  STAT_ATTR(FREE_ADD_PARTIAL, free_add_partial);
>  STAT_ATTR(FREE_REMOVE_PARTIAL, free_remove_partial);
>  STAT_ATTR(ALLOC_FROM_PARTIAL, alloc_from_partial);
> @@ -8826,7 +8813,6 @@ static struct attribute *slab_attrs[] = {
>         &free_rcu_sheaf_fail_attr.attr,
>         &free_fastpath_attr.attr,
>         &free_slowpath_attr.attr,
> -       &free_frozen_attr.attr,
>         &free_add_partial_attr.attr,
>         &free_remove_partial_attr.attr,
>         &alloc_from_partial_attr.attr,
>
> --
> 2.52.0
>