[PATCH RFC v2 18/20] slab: remove frozen slab checks from __slab_free()

[Vlastimil Babka <vbabka@suse.cz>]

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@suse.cz>
---
 mm/slub.c | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 7f675659d93b..5b2d7c387646 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 */
@@ -5093,7 +5092,7 @@ 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;
@@ -5116,7 +5115,6 @@ 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);
 
@@ -5129,7 +5127,7 @@ 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));
 			/*
@@ -5148,20 +5146,10 @@ 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;
 	}
 
@@ -8715,7 +8703,6 @@ 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);
@@ -8820,7 +8807,6 @@ 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