[PATCH v2 19/28] mm: memcg/slab: deprecate memory.kmem.slabinfo

[Roman Gushchin <guro@fb.com>]

Deprecate memory.kmem.slabinfo.

An empty file will be presented if corresponding config options are
enabled.

The interface is implementation dependent, isn't present in cgroup v2,
and is generally useful only for core mm debugging purposes. In other
words, it doesn't provide any value for the absolute majority of users.

A drgn-based replacement can be found in tools/cgroup/slabinfo.py .
It does support cgroup v1 and v2, mimics memory.kmem.slabinfo output
and also allows to get any additional information without a need
to recompile the kernel.

If a drgn-based solution is too slow for a task, a bpf-based tracing
tool can be used, which can easily keep track of all slab allocations
belonging to a memory cgroup.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 mm/memcontrol.c  |  3 ---
 mm/slab_common.c | 31 ++++---------------------------
 2 files changed, 4 insertions(+), 30 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0e9fe272e688..45bd9b1d9735 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5013,9 +5013,6 @@ static struct cftype mem_cgroup_legacy_files[] = {
 #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
 	{
 		.name = "kmem.slabinfo",
-		.seq_start = memcg_slab_start,
-		.seq_next = memcg_slab_next,
-		.seq_stop = memcg_slab_stop,
 		.seq_show = memcg_slab_show,
 	},
 #endif
diff --git a/mm/slab_common.c b/mm/slab_common.c
index a2afa4ff5d7b..80b4efdb1df3 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1522,35 +1522,12 @@ void dump_unreclaimable_slab(void)
 }
 
 #if defined(CONFIG_MEMCG)
-void *memcg_slab_start(struct seq_file *m, loff_t *pos)
-{
-	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
-
-	mutex_lock(&slab_mutex);
-	return seq_list_start(&memcg->kmem_caches, *pos);
-}
-
-void *memcg_slab_next(struct seq_file *m, void *p, loff_t *pos)
-{
-	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
-
-	return seq_list_next(p, &memcg->kmem_caches, pos);
-}
-
-void memcg_slab_stop(struct seq_file *m, void *p)
-{
-	mutex_unlock(&slab_mutex);
-}
-
 int memcg_slab_show(struct seq_file *m, void *p)
 {
-	struct kmem_cache *s = list_entry(p, struct kmem_cache,
-					  memcg_params.kmem_caches_node);
-	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
-
-	if (p == memcg->kmem_caches.next)
-		print_slabinfo_header(m);
-	cache_show(s, m);
+	/*
+	 * Deprecated.
+	 * Please, take a look at tools/cgroup/slabinfo.py .
+	 */
 	return 0;
 }
 #endif
-- 
2.24.1