[PATCH v4 20/22] slab: remove frozen slab checks from __slab_free()

Vlastimil Babka
2026-01-23T06:54:16Z

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>
Reviewed-by: Hao Li <hao.li@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 22 ++++------------------
1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index d9fc56122975..3009eb7bd8d2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -338,7 +338,6 @@ 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 */
@@ -5109,7 +5108,7 @@ 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;
@@ -5132,7 +5131,6 @@ 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);

@@ -5145,7 +5143,7 @@ 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));
/*
@@ -5164,20 +5162,10 @@ 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;
}

@@ -8753,7 +8741,6 @@ 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);
@@ -8858,7 +8845,6 @@ 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