writeback: add debug info for memcg-blkcg link

Signed-off-by: NJiufei Xue <jiufei.xue@linux.alibaba.com>
Reviewed-by: NJoseph Qi <joseph.qi@linux.alibaba.com>

include/trace/events/writeback.h

@@ -303,6 +303,27 @@ TRACE_EVENT(writeback_bdi_register,
 	)
 );
 
+TRACE_EVENT(insert_memcg_blkcg_link,
+	TP_PROTO(struct cgroup_subsys_state *memcg_css,
+		 struct cgroup_subsys_state *blkcg_css,
+		 struct cgroup_subsys_state *old_blkcg_css),
+	TP_ARGS(memcg_css, blkcg_css, old_blkcg_css),
+	TP_STRUCT__entry(
+		__field(unsigned int, memcg_ino)
+		__field(unsigned int, blkcg_ino)
+		__field(unsigned int, old_blkcg_ino)
+	),
+	TP_fast_assign(
+		__entry->memcg_ino = memcg_css->cgroup->kn->id.ino;
+		__entry->blkcg_ino = blkcg_css->cgroup->kn->id.ino;
+		__entry->old_blkcg_ino = old_blkcg_css ?
+			        old_blkcg_css->cgroup->kn->id.ino : 0;
+	),
+	TP_printk("memcg_ino=%u blkcg_ino=%u old_blkcg_ino=%u",
+		  __entry->memcg_ino, __entry->blkcg_ino, __entry->old_blkcg_ino
+	)
+);
+
 DECLARE_EVENT_CLASS(wbc_class,
 	TP_PROTO(struct writeback_control *wbc, struct backing_dev_info *bdi),
 	TP_ARGS(wbc, bdi),

mm/backing-dev.c

@@ -36,9 +36,22 @@ struct workqueue_struct *bdi_wq;
 
 static struct dentry *bdi_debug_root;
 
+#ifdef CONFIG_CGROUP_WRITEBACK
+static struct dentry *memcg_blkcg_file;
+static const struct file_operations memcg_blkcg_debug_fops;
+#endif
+
 static void bdi_debug_init(void)
 {
 	bdi_debug_root = debugfs_create_dir("bdi", NULL);
+
+#ifdef CONFIG_CGROUP_WRITEBACK
+	if (!bdi_debug_root)
+		return;
+
+	memcg_blkcg_file = debugfs_create_file("bdi_wb_link", 0444, bdi_debug_root,
+			NULL, &memcg_blkcg_debug_fops);
+#endif
 }
 
 static int bdi_debug_stats_show(struct seq_file *m, void *v)
@@ -403,6 +416,40 @@ struct memcg_blkcg_link {
 static RADIX_TREE(memcg_blkcg_tree, GFP_ATOMIC);
 DEFINE_SPINLOCK(memcg_blkcg_tree_lock);
 
+static int memcg_blkcg_link_show(struct seq_file *m, void *v)
+{
+	struct memcg_blkcg_link *link;
+	struct radix_tree_iter iter;
+	void **slot;
+
+	seq_printf(m, "memory     <--->     blkio\n");
+	rcu_read_lock();
+	radix_tree_for_each_slot(slot, &memcg_blkcg_tree, &iter, 0) {
+		link = *slot;
+		seq_printf(m, "%s:%5u <---> %s:%5u\n",
+				link->memcg_css->cgroup->kn->name,
+				link->memcg_css->cgroup->kn->id.ino,
+				(link->blkcg_css == blkcg_root_css) ?
+				"root" : link->blkcg_css->cgroup->kn->name,
+				link->blkcg_css->cgroup->kn->id.ino);
+	}
+	rcu_read_unlock();
+
+	return 0;
+}
+
+static int memcg_blkcg_link_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, memcg_blkcg_link_show, inode->i_private);
+}
+
+static const struct file_operations memcg_blkcg_debug_fops = {
+	.open		= memcg_blkcg_link_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 int allocate_memcg_blkcg_links(int count, struct list_head *tmp_links)
 {
 	struct memcg_blkcg_link *link;
@@ -456,6 +503,9 @@ void insert_memcg_blkcg_link(struct cgroup_subsys *ss,
 	}
 	rcu_read_unlock();
 
+	trace_insert_memcg_blkcg_link(memcg_css, blkcg_css,
+		link ? link->blkcg_css : NULL);
+
 	spin_lock(&memcg_blkcg_tree_lock);
 	if (link) {
 		radix_tree_delete(&memcg_blkcg_tree, memcg_css->id);