[PATCH 13/12] memcg: don't need memcg->memcg_name

[Li Zefan]

Now memcg has the same life cycle as its corresponding cgroup,
we don't have to save the cgroup path name in memcg->memcg_name.

Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
---
 mm/memcontrol.c | 65 +++++++++++++++++++++------------------------------------
 1 file changed, 24 insertions(+), 41 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aeab1d3..06e995e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -306,20 +306,12 @@ struct mem_cgroup {
 		struct list_head dead;
 	};
 
-	union {
-		/*
-		 * Should we move charges of a task when a task is moved into
-		 * this mem_cgroup ? And what type of charges should we move ?
-		 */
-		unsigned long move_charge_at_immigrate;
+	/*
+	 * Should we move charges of a task when a task is moved into
+	 * this mem_cgroup ? And what type of charges should we move ?
+	 */
+	unsigned long move_charge_at_immigrate;
 
-		/*
-		 * We are no longer concerned about moving charges after memcg
-		 * is dead. So we will fill this up with its name, to aid
-		 * debugging.
-		 */
-		char *memcg_name;
-	};
 	/*
 	 * set > 0 if pages under this cgroup are moving to other cgroup.
 	 */
@@ -381,36 +373,10 @@ static inline void memcg_dangling_free(struct mem_cgroup *memcg)
 	mutex_lock(&dangling_memcgs_mutex);
 	list_del(&memcg->dead);
 	mutex_unlock(&dangling_memcgs_mutex);
-	free_pages((unsigned long)memcg->memcg_name, 0);
 }
 
 static inline void memcg_dangling_add(struct mem_cgroup *memcg)
 {
-	/*
-	 * cgroup.c will do page-sized allocations most of the time,
-	 * so we'll just follow the pattern. Also, __get_free_pages
-	 * is a better interface than kmalloc for us here, because
-	 * we'd like this memory to be always billed to the root cgroup,
-	 * not to the process removing the memcg. While kmalloc would
-	 * require us to wrap it into memcg_stop/resume_kmem_account,
-	 * with __get_free_pages we just don't pass the memcg flag.
-	 */
-	memcg->memcg_name = (char *)__get_free_pages(GFP_KERNEL, 0);
-
-	/*
-	 * we will, in general, just ignore failures. No need to go crazy,
-	 * being this just a debugging interface. It is nice to copy a memcg
-	 * name over, but if we (unlikely) can't, just the address will do
-	 */
-	if (!memcg->memcg_name)
-		goto add_list;
-
-	if (cgroup_path(memcg->css.cgroup, memcg->memcg_name, PAGE_SIZE) < 0) {
-		free_pages((unsigned long)memcg->memcg_name, 0);
-		memcg->memcg_name = NULL;
-	}
-
-add_list:
 	INIT_LIST_HEAD(&memcg->dead);
 	mutex_lock(&dangling_memcgs_mutex);
 	list_add(&memcg->dead, &dangling_memcgs);
@@ -5188,12 +5154,28 @@ static int mem_cgroup_dangling_read(struct cgroup *cont, struct cftype *cft,
 					struct seq_file *m)
 {
 	struct mem_cgroup *memcg;
+	char *memcg_name;
+	int ret;
+
+	/*
+	 * cgroup.c will do page-sized allocations most of the time,
+	 * so we'll just follow the pattern. Also, __get_free_pages
+	 * is a better interface than kmalloc for us here, because
+	 * we'd like this memory to be always billed to the root cgroup,
+	 * not to the process removing the memcg. While kmalloc would
+	 * require us to wrap it into memcg_stop/resume_kmem_account,
+	 * with __get_free_pages we just don't pass the memcg flag.
+	 */
+	memcg_name = (char *)__get_free_pages(GFP_KERNEL, 0);
+	if (!memcg_name)
+		return -ENOMEM;
 
 	mutex_lock(&dangling_memcgs_mutex);
 
 	list_for_each_entry(memcg, &dangling_memcgs, dead) {
-		if (memcg->memcg_name)
-			seq_printf(m, "%s:\n", memcg->memcg_name);
+		ret = cgroup_path(memcg->css.cgroup, memcg_name, PAGE_SIZE);
+		if (!ret)
+			seq_printf(m, "%s:\n", memcg_name);
 		else
 			seq_printf(m, "%p (name lost):\n", memcg);
 
@@ -5203,6 +5185,7 @@ static int mem_cgroup_dangling_read(struct cgroup *cont, struct cftype *cft,
 	}
 
 	mutex_unlock(&dangling_memcgs_mutex);
+	free_pages((unsigned long)memcg_name, 0);
 	return 0;
 }
 #endif
-- 
1.8.0.2
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