mm: memcg/slab: use a single set of kmem_caches for all accounted allocations

This is fairly big but mostly red patch, which makes all accounted slab
allocations use a single set of kmem_caches instead of creating a separate
set for each memory cgroup.

Because the number of non-root kmem_caches is now capped by the number of
root kmem_caches, there is no need to shrink or destroy them prematurely.
They can be perfectly destroyed together with their root counterparts.
This allows to dramatically simplify the management of non-root
kmem_caches and delete a ton of code.

This patch performs the following changes:
1) introduces memcg_params.memcg_cache pointer to represent the
   kmem_cache which will be used for all non-root allocations
2) reuses the existing memcg kmem_cache creation mechanism
   to create memcg kmem_cache on the first allocation attempt
3) memcg kmem_caches are named <kmemcache_name>-memcg,
   e.g. dentry-memcg
4) simplifies memcg_kmem_get_cache() to just return memcg kmem_cache
   or schedule it's creation and return the root cache
5) removes almost all non-root kmem_cache management code
   (separate refcounter, reparenting, shrinking, etc)
6) makes slab debugfs to display root_mem_cgroup css id and never
   show :dead and :deact flags in the memcg_slabinfo attribute.

Following patches in the series will simplify the kmem_cache creation.

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/20200623174037.3951353-13-guro@fb.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 13 deletions

diff --git a/mm/slab.c b/mm/slab.c
index 1e90b67735aa..0dd6956585dc 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1249,7 +1249,7 @@ void __init kmem_cache_init(void)
 				  nr_node_ids * sizeof(struct kmem_cache_node *),
 				  SLAB_HWCACHE_ALIGN, 0, 0);
 	list_add(&kmem_cache->list, &slab_caches);
-	memcg_link_cache(kmem_cache, NULL);
+	memcg_link_cache(kmem_cache);
 	slab_state = PARTIAL;
 
 	/*
@@ -2253,17 +2253,6 @@ int __kmem_cache_shrink(struct kmem_cache *cachep)
 	return (ret ? 1 : 0);
 }
 
-#ifdef CONFIG_MEMCG
-void __kmemcg_cache_deactivate(struct kmem_cache *cachep)
-{
-	__kmem_cache_shrink(cachep);
-}
-
-void __kmemcg_cache_deactivate_after_rcu(struct kmem_cache *s)
-{
-}
-#endif
-
 int __kmem_cache_shutdown(struct kmem_cache *cachep)
 {
 	return __kmem_cache_shrink(cachep);
@@ -3872,7 +3861,8 @@ static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
 		return ret;
 
 	lockdep_assert_held(&slab_mutex);
-	for_each_memcg_cache(c, cachep) {
+	c = memcg_cache(cachep);
+	if (c) {
 		/* return value determined by the root cache only */
 		__do_tune_cpucache(c, limit, batchcount, shared, gfp);
 	}