[PATCH-next v2] mm, memcg: Add ":deact" tag for reparented kmem caches in memcg_slabinfo

[Waiman Long <longman@xxxxxxxxxx>]

With Roman's kmem cache reparent patch, multiple kmem caches of the same
type can be seen attached to the same memcg id. All of them, except
maybe one, are reparent'ed kmem caches. It can be useful to tag those
reparented caches by adding a new slab flag "SLAB_DEACTIVATED" to those
kmem caches that will be reparent'ed if it cannot be destroyed completely.

For the reparent'ed memcg kmem caches, the tag ":deact" will now be
shown in <debugfs>/memcg_slabinfo.

[v2: Set the flag in the common code as suggested by Roman.]

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
---
 include/linux/slab.h |  4 ++++
 mm/slab_common.c     | 15 +++++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index fecf40b7be69..19ab1380f875 100644
--- a/include/linux/slab.h
+++ b/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.
  *
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 146d8eaa639c..464faaa9fd81 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -771,6 +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
@@ -1533,7 +1534,7 @@ static int memcg_slabinfo_show(struct seq_file *m, void *unused)
 	struct slabinfo sinfo;
 
 	mutex_lock(&slab_mutex);
-	seq_puts(m, "# <name> <css_id[:dead]> <active_objs> <num_objs>");
+	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) {
 		/*
@@ -1544,22 +1545,24 @@ static int memcg_slabinfo_show(struct seq_file *m, void *unused)
 
 		memset(&sinfo, 0, sizeof(sinfo));
 		get_slabinfo(s, &sinfo);
-		seq_printf(m, "%-17s root      %6lu %6lu %6lu %6lu\n",
+		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 *dead = "";
+			char *status = "";
 
 			css = &c->memcg_params.memcg->css;
 			if (!(css->flags & CSS_ONLINE))
-				dead = ":dead";
+				status = ":dead";
+			else if (c->flags & SLAB_DEACTIVATED)
+				status = ":deact";
 
 			memset(&sinfo, 0, sizeof(sinfo));
 			get_slabinfo(c, &sinfo);
-			seq_printf(m, "%-17s %4d%5s %6lu %6lu %6lu %6lu\n",
-				   cache_name(c), css->id, dead,
+			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);
 		}
-- 
2.18.1