[PATCH] mm, memcg: Add a memcg_slabinfo debugfs file

[Waiman Long <longman@redhat.com>]

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 cgroup removal. Therefore, it will be useful to show how many
memcg caches are present for each of the kmem caches.

This patch introduces a new <debugfs>/memcg_slabinfo file which is
somewhat similar to /proc/slabinfo in format, but lists only slabs that
are in 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> <active_objs> <num_objs> <active_slabs> <num_slabs> <num_caches> <num_empty_caches>
  rpc_inode_cache        0      0      0      0   1   1
  xfs_inode           6342   7888    232    232  59  13
  RAWv6                  0      0      0      0   2   2
  UDPv6                100    100      4      4   5   3
  TCPv6                  0      0      0      0   1   1
  UNIX                4864   4864    152    152  53  35
  RAW                    0      0      0      0   1   1
  TCP                   14     14      1      1   2   1

Besides the number of objects and slabs in the memcg kmem caches only,
it also shows the total number of memcg kmem caches associated with each
root kmem cache as well as the number memcg kmem caches that are empty.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/slab_common.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 58251ba63e4a..63fb18f4f811 100644
--- a/mm/slab_common.c
+++ b/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>
@@ -1498,6 +1499,58 @@ static int __init slab_proc_init(void)
 	return 0;
 }
 module_init(slab_proc_init);
+
+#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_MEMCG)
+/*
+ * Display information about slabs that are in memcg kmem caches, but not
+ * in the root kmem caches.
+ */
+static int memcg_slabinfo_show(struct seq_file *m, void *unused)
+{
+	struct kmem_cache *s, *c;
+	struct slabinfo sinfo, cinfo;
+
+	mutex_lock(&slab_mutex);
+	seq_puts(m, "# <name> <active_objs> <num_objs> <active_slabs>");
+	seq_puts(m, " <num_slabs> <num_caches> <num_empty_caches>\n");
+	memset(&sinfo, 0, sizeof(sinfo));
+	list_for_each_entry(s, &slab_root_caches, root_caches_node) {
+		int scnt = 0;	/* memcg kmem cache count */
+		int ecnt = 0;	/* # of empty kmem caches */
+
+		for_each_memcg_cache(c, s) {
+			memset(&cinfo, 0, sizeof(cinfo));
+			get_slabinfo(c, &cinfo);
+
+			sinfo.active_slabs += cinfo.active_slabs;
+			sinfo.num_slabs += cinfo.num_slabs;
+			sinfo.active_objs += cinfo.active_objs;
+			sinfo.num_objs += cinfo.num_objs;
+			scnt++;
+			if (!cinfo.num_slabs)
+				ecnt++;
+		}
+		if (!scnt)
+			continue;
+		seq_printf(m, "%-17s %6lu %6lu %6lu %6lu %3d %3d\n",
+			   cache_name(s), sinfo.active_objs, sinfo.num_objs,
+			   sinfo.active_slabs, sinfo.num_slabs, scnt, ecnt);
+		memset(&sinfo, 0, sizeof(sinfo));
+	}
+	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 */
 #endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */
 
 static __always_inline void *__do_krealloc(const void *p, size_t new_size,
-- 
2.18.1