slab: link memcg caches of the same kind into a list

Sometimes, we need to iterate over all memcg copies of a particular root
kmem cache.  Currently, we use memcg_cache_params->memcg_caches array for
that, because it contains all existing memcg caches.

However, it's a bad practice to keep all caches, including those that
belong to offline cgroups, in this array, because it will be growing
beyond any bounds then.  I'm going to wipe away dead caches from it to
save space.  To still be able to perform iterations over all memcg caches
of the same kind, let us link them into a list.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/mm/slab.h b/mm/slab.h
index 53a623f85931..0a56d76ac0e9 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -163,6 +163,18 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
                        size_t count, loff_t *ppos);
 
 #ifdef CONFIG_MEMCG_KMEM
+/*
+ * Iterate over all memcg caches of the given root cache. The caller must hold
+ * slab_mutex.
+ */
+#define for_each_memcg_cache(iter, root) \
+        list_for_each_entry(iter, &(root)->memcg_params.list, \
+                            memcg_params.list)
+
+#define for_each_memcg_cache_safe(iter, tmp, root) \
+        list_for_each_entry_safe(iter, tmp, &(root)->memcg_params.list, \
+                                 memcg_params.list)
+
 static inline bool is_root_cache(struct kmem_cache *s)
 {
         return s->memcg_params.is_root_cache;
@@ -241,6 +253,11 @@ extern void slab_init_memcg_params(struct kmem_cache *);
 
 #else /* !CONFIG_MEMCG_KMEM */
 
+#define for_each_memcg_cache(iter, root) \
+        for ((void)(iter), (void)(root); 0; )
+#define for_each_memcg_cache_safe(iter, tmp, root) \
+        for ((void)(iter), (void)(tmp), (void)(root); 0; )
+
 static inline bool is_root_cache(struct kmem_cache *s)
 {
         return true;