linux-kernel - [PATCH RFC 19/19] slab: remove frozen slab checks from __slab

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Message-Id: <20251023-sheaves-for-all-v1-19-6ffa2c9941c0@suse.cz>
Date: Thu, 23 Oct 2025 15:52:41 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>
Cc: Uladzislau Rezki <urezki@...il.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Suren Baghdasaryan <surenb@...gle.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
 bpf@...r.kernel.org, kasan-dev@...glegroups.com, 
 Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH RFC 19/19] slab: remove frozen slab checks from
 __slab_free()

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.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 515a2b59cb52..9b551c48c2eb 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -336,7 +336,6 @@ 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 */
@@ -5036,7 +5035,6 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,

 {
 	void *prior;
-	int was_frozen;
 	struct slab new;
 	unsigned long counters;
 	struct kmem_cache_node *n = NULL;
@@ -5059,9 +5057,8 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
 		counters = slab->counters;
 		set_freepointer(s, tail, prior);
 		new.counters = counters;
-		was_frozen = new.frozen;
 		new.inuse -= cnt;
-		if ((!new.inuse || !prior) && !was_frozen) {
+		if (!new.inuse || !prior) {
 			/* Needs to be taken off a list */
 			n = get_node(s, slab_nid(slab));
 			/*
@@ -5083,15 +5080,10 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
 		"__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);
-		}
-
+		/*
+		 * The list lock was not taken therefore no list activity can be
+		 * necessary.
+		 */
 		return;
 	}

@@ -8648,7 +8640,6 @@ 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);
@@ -8753,7 +8744,6 @@ 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,

-- 
2.51.1