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

Suren Baghdasaryan
2026-01-22T00:54:22Z

On Fri, Jan 16, 2026 at 2:41 PM Vlastimil Babka <vbabka@suse.cz> 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@google.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

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@google.com>

> ---
> 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
>