mm: memcg/slab: deprecate slab_root_caches

Currently there are two lists of kmem_caches:
1) slab_caches, which contains all kmem_caches,
2) slab_root_caches, which contains only root kmem_caches.

And there is some preprocessor magic to have a single list if
CONFIG_MEMCG_KMEM isn't enabled.

It was required earlier because the number of non-root kmem_caches was
proportional to the number of memory cgroups and could reach really big
values.  Now, when it cannot exceed the number of root kmem_caches, there
is really no reason to maintain two lists.

We never iterate over the slab_root_caches list on any hot paths, so it's
perfectly fine to iterate over slab_caches and filter out non-root
kmem_caches.

It allows to remove a lot of config-dependent code and two pointers from
the kmem_cache structure.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/20200623174037.3951353-16-guro@fb.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 29 deletions

diff --git a/mm/slab_common.c b/mm/slab_common.c
index de0a46cf974a..a9f6ab452ce5 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -131,9 +131,6 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t nr,
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-
-LIST_HEAD(slab_root_caches);
-
 static void memcg_kmem_cache_create_func(struct work_struct *work)
 {
 	struct kmem_cache *cachep = container_of(work, struct kmem_cache,
@@ -156,27 +153,11 @@ static void init_memcg_params(struct kmem_cache *s,
 	else
 		slab_init_memcg_params(s);
 }
-
-void memcg_link_cache(struct kmem_cache *s)
-{
-	if (is_root_cache(s))
-		list_add(&s->root_caches_node, &slab_root_caches);
-}
-
-static void memcg_unlink_cache(struct kmem_cache *s)
-{
-	if (is_root_cache(s))
-		list_del(&s->root_caches_node);
-}
 #else
 static inline void init_memcg_params(struct kmem_cache *s,
 				     struct kmem_cache *root_cache)
 {
 }
-
-static inline void memcg_unlink_cache(struct kmem_cache *s)
-{
-}
 #endif /* CONFIG_MEMCG_KMEM */
 
 /*
@@ -253,7 +234,7 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align,
 	if (flags & SLAB_NEVER_MERGE)
 		return NULL;
 
-	list_for_each_entry_reverse(s, &slab_root_caches, root_caches_node) {
+	list_for_each_entry_reverse(s, &slab_caches, list) {
 		if (slab_unmergeable(s))
 			continue;
 
@@ -312,7 +293,6 @@ static struct kmem_cache *create_cache(const char *name,
 
 	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
-	memcg_link_cache(s);
 out:
 	if (err)
 		return ERR_PTR(err);
@@ -507,7 +487,6 @@ static int shutdown_cache(struct kmem_cache *s)
 	if (__kmem_cache_shutdown(s) != 0)
 		return -EBUSY;
 
-	memcg_unlink_cache(s);
 	list_del(&s->list);
 
 	if (s->flags & SLAB_TYPESAFE_BY_RCU) {
@@ -751,7 +730,6 @@ struct kmem_cache *__init create_kmalloc_cache(const char *name,
 
 	create_boot_cache(s, name, size, flags, useroffset, usersize);
 	list_add(&s->list, &slab_caches);
-	memcg_link_cache(s);
 	s->refcount = 1;
 	return s;
 }
@@ -1107,12 +1085,12 @@ static void print_slabinfo_header(struct seq_file *m)
 void *slab_start(struct seq_file *m, loff_t *pos)
 {
 	mutex_lock(&slab_mutex);
-	return seq_list_start(&slab_root_caches, *pos);
+	return seq_list_start(&slab_caches, *pos);
 }
 
 void *slab_next(struct seq_file *m, void *p, loff_t *pos)
 {
-	return seq_list_next(p, &slab_root_caches, pos);
+	return seq_list_next(p, &slab_caches, pos);
 }
 
 void slab_stop(struct seq_file *m, void *p)
@@ -1165,11 +1143,12 @@ static void cache_show(struct kmem_cache *s, struct seq_file *m)
 
 static int slab_show(struct seq_file *m, void *p)
 {
-	struct kmem_cache *s = list_entry(p, struct kmem_cache, root_caches_node);
+	struct kmem_cache *s = list_entry(p, struct kmem_cache, list);
 
-	if (p == slab_root_caches.next)
+	if (p == slab_caches.next)
 		print_slabinfo_header(m);
-	cache_show(s, m);
+	if (is_root_cache(s))
+		cache_show(s, m);
 	return 0;
 }
 
@@ -1271,7 +1250,7 @@ static int memcg_slabinfo_show(struct seq_file *m, void *unused)
 	mutex_lock(&slab_mutex);
 	seq_puts(m, "# <name> <css_id[:dead|deact]> <active_objs> <num_objs>");
 	seq_puts(m, " <active_slabs> <num_slabs>\n");
-	list_for_each_entry(s, &slab_root_caches, root_caches_node) {
+	list_for_each_entry(s, &slab_caches, list) {
 		/*
 		 * Skip kmem caches that don't have the memcg cache.
 		 */