mm, memcg: add a memcg_slabinfo debugfs file

There are concerns about memory leaks from extensive use of memory cgroups
as each memory cgroup creates its own set of kmem caches.  There is a
possiblity that the memcg kmem caches may remain even after the memory
cgroups have been offlined.  Therefore, it will be useful to show the
status of each of memcg kmem caches.

This patch introduces a new <debugfs>/memcg_slabinfo file which is
somewhat similar to /proc/slabinfo in format, but lists only information
about kmem caches that have child memcg kmem caches.  Information
available in /proc/slabinfo are not repeated in memcg_slabinfo.

A portion of a sample output of the file was:

  # <name> <css_id[:dead]> <active_objs> <num_objs> <active_slabs> <num_slabs>
  rpc_inode_cache   root          13     51      1      1
  rpc_inode_cache     48           0      0      0      0
  fat_inode_cache   root           1     45      1      1
  fat_inode_cache     41           2     45      1      1
  xfs_inode         root         770    816     24     24
  xfs_inode           92          22     34      1      1
  xfs_inode           88:dead      1     34      1      1
  xfs_inode           89:dead     23     34      1      1
  xfs_inode           85           4     34      1      1
  xfs_inode           84           9     34      1      1

The css id of the memcg is also listed. If a memcg is not online,
the tag ":dead" will be attached as shown above.

[longman@redhat.com: memcg: add ":deact" tag for reparented kmem caches in memcg_slabinfo]
  Link: http://lkml.kernel.org/r/20190621173005.31514-1-longman@redhat.com
[longman@redhat.com: set the flag in the common code as suggested by Roman]
  Link: http://lkml.kernel.org/r/20190627184324.5875-1-longman@redhat.com
Link: http://lkml.kernel.org/r/20190619171621.26209-1-longman@redhat.comSigned-off-by: Waiman Long <longman@redhat.com>
Suggested-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slab.h

@@ -116,6 +116,10 @@
 /* Objects are reclaimable */
 #define SLAB_RECLAIM_ACCOUNT	((slab_flags_t __force)0x00020000U)
 #define SLAB_TEMPORARY		SLAB_RECLAIM_ACCOUNT	/* Objects are short-lived */
+
+/* Slab deactivation flag */
+#define SLAB_DEACTIVATED	((slab_flags_t __force)0x10000000U)
+
 /*
  * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests.
  *

mm/slab_common.c

@@ -17,6 +17,7 @@
 #include <linux/uaccess.h>
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
+#include <linux/debugfs.h>
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
 #include <asm/page.h>
@@ -770,6 +771,7 @@ static void kmemcg_cache_deactivate(struct kmem_cache *s)
 		return;
 
 	__kmemcg_cache_deactivate(s);
+	s->flags |= SLAB_DEACTIVATED;
 
 	/*
 	 * memcg_kmem_wq_lock is used to synchronize memcg_params.dying
@@ -1521,6 +1523,64 @@ static int __init slab_proc_init(void)
 	return 0;
 }
 module_init(slab_proc_init);
+
+#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_MEMCG_KMEM)
+/*
+ * Display information about kmem caches that have child memcg caches.
+ */
+static int memcg_slabinfo_show(struct seq_file *m, void *unused)
+{
+	struct kmem_cache *s, *c;
+	struct slabinfo sinfo;
+
+	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) {
+		/*
+		 * Skip kmem caches that don't have any memcg children.
+		 */
+		if (list_empty(&s->memcg_params.children))
+			continue;
+
+		memset(&sinfo, 0, sizeof(sinfo));
+		get_slabinfo(s, &sinfo);
+		seq_printf(m, "%-17s root       %6lu %6lu %6lu %6lu\n",
+			   cache_name(s), sinfo.active_objs, sinfo.num_objs,
+			   sinfo.active_slabs, sinfo.num_slabs);
+
+		for_each_memcg_cache(c, s) {
+			struct cgroup_subsys_state *css;
+			char *status = "";
+
+			css = &c->memcg_params.memcg->css;
+			if (!(css->flags & CSS_ONLINE))
+				status = ":dead";
+			else if (c->flags & SLAB_DEACTIVATED)
+				status = ":deact";
+
+			memset(&sinfo, 0, sizeof(sinfo));
+			get_slabinfo(c, &sinfo);
+			seq_printf(m, "%-17s %4d%-6s %6lu %6lu %6lu %6lu\n",
+				   cache_name(c), css->id, status,
+				   sinfo.active_objs, sinfo.num_objs,
+				   sinfo.active_slabs, sinfo.num_slabs);
+		}
+	}
+	mutex_unlock(&slab_mutex);
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(memcg_slabinfo);
+
+static int __init memcg_slabinfo_init(void)
+{
+	debugfs_create_file("memcg_slabinfo", S_IFREG | S_IRUGO,
+			    NULL, NULL, &memcg_slabinfo_fops);
+	return 0;
+}
+
+late_initcall(memcg_slabinfo_init);
+#endif /* CONFIG_DEBUG_FS && CONFIG_MEMCG_KMEM */
 #endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */
 
 static __always_inline void *__do_krealloc(const void *p, size_t new_size,