[-mm patch] Show memcg information during OOM (v2)

[Balbir Singh]

Description: Add RSS and swap to OOM output from memcg

From: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>

Changelog v2..v1:

1. Add more information about task's memcg and the memcg
   over it's limit
2. Print data in KB
3. Move the print routine outside task_lock()
4. Use rcu_read_lock() around cgroup_path, strictly speaking it
   is not required, but relying on the current memcg implementation
   is not a good idea.

This patch displays memcg values like failcnt, usage and limit
when an OOM occurs due to memcg.

NOTE: In case the path exceeds 128 bytes, we omit printing the
name of the cgroups. It is possible to circumvent this problem
by using static arrays of PAGE_SIZE and we know that OOM is
serialized when invoked from the memory controller. This did
not seem like a good idea, but can be implemented if 128 bytes
seems like a severe limitation.

Thanks go out to Johannes Weiner, Li Zefan, David Rientjes,
Kamezawa Hiroyuki, Daisuke Nishimura and KOSAKI Motohiro for
review.

Sample output
-------------

Task in /a/x killed as a result of limit of /a
memory: usage 1048576kB, limit 1048576kB, failcnt 4183
memory+swap: usage 1400964kB, limit 9007199254740991kB, failcnt 0

Signed-off-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
---

 include/linux/memcontrol.h |    6 ++++
 mm/memcontrol.c            |   61 ++++++++++++++++++++++++++++++++++++++++++++
 mm/oom_kill.c              |    1 +
 3 files changed, 68 insertions(+), 0 deletions(-)


diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 326f45c..56f1af2 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -104,6 +104,8 @@ struct zone_reclaim_stat *mem_cgroup_get_reclaim_stat(struct mem_cgroup *memcg,
 						      struct zone *zone);
 struct zone_reclaim_stat*
 mem_cgroup_get_reclaim_stat_from_page(struct page *page);
+extern void mem_cgroup_print_mem_info(struct mem_cgroup *memcg,
+					struct task_struct *p);
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 extern int do_swap_account;
@@ -270,6 +272,10 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
 	return NULL;
 }
 
+void mem_cgroup_print_mem_info(struct mem_cgroup *memcg, struct task_struct *p)
+{
+}
+
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8e4be9c..e7f82b6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -42,6 +42,7 @@
 
 struct cgroup_subsys mem_cgroup_subsys __read_mostly;
 #define MEM_CGROUP_RECLAIM_RETRIES	5
+#define MEM_CGROUP_OOM_BUF_SIZE		128
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 /* Turned on only when memory cgroup is enabled && really_do_swap_account = 0 */
@@ -813,6 +814,66 @@ bool mem_cgroup_oom_called(struct task_struct *task)
 	rcu_read_unlock();
 	return ret;
 }
+
+/**
+ * mem_cgroup_print_mem_info: Called from OOM with tasklist_lock held in
+ * read mode.
+ * @memcg: The memory cgroup that went over limit
+ * @p: Task that is going to be killed
+ *
+ * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
+ * enabled
+ */
+void mem_cgroup_print_mem_info(struct mem_cgroup *memcg, struct task_struct *p)
+{
+	struct cgroup *task_cgrp;
+	struct cgroup *mem_cgrp;
+	/*
+	 * Need a buffer on stack, can't rely on allocations.
+	 */
+	char task_memcg_name[MEM_CGROUP_OOM_BUF_SIZE];
+	char memcg_name[MEM_CGROUP_OOM_BUF_SIZE];
+	int ret;
+
+	if (!memcg)
+		return;
+
+	mem_cgrp = memcg->css.cgroup;
+	task_cgrp = mem_cgroup_from_task(p)->css.cgroup;
+
+	rcu_read_lock();
+	ret = cgroup_path(task_cgrp, task_memcg_name, MEM_CGROUP_OOM_BUF_SIZE);
+	if (ret < 0) {
+		/*
+		 * Unfortunately, we are unable to convert to a useful name
+		 * But we'll still print out the usage information
+		 */
+		rcu_read_unlock();
+		goto done;
+	}
+	ret = cgroup_path(mem_cgrp, memcg_name, MEM_CGROUP_OOM_BUF_SIZE);
+	 if (ret < 0) {
+		rcu_read_unlock();
+		goto done;
+	}
+
+	rcu_read_unlock();
+
+	printk(KERN_INFO "Task in %s killed as a result of limit of %s\n",
+			task_memcg_name, memcg_name);
+done:
+
+	printk(KERN_INFO "memory: usage %llukB, limit %llukB, failcnt %llu\n",
+		res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
+		res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
+		res_counter_read_u64(&memcg->res, RES_FAILCNT));
+	printk(KERN_INFO "memory+swap: usage %llukB, limit %llukB, "
+		"failcnt %llu\n", 
+		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
+		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
+		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
+}
+
 /*
  * Unlike exported interface, "oom" parameter is added. if oom==true,
  * oom-killer can be invoked.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d3b9bac..951356f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -394,6 +394,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		cpuset_print_task_mems_allowed(current);
 		task_unlock(current);
 		dump_stack();
+		mem_cgroup_print_mem_info(mem, current);
 		show_mem();
 		if (sysctl_oom_dump_tasks)
 			dump_tasks(mem);

-- 
	Balbir
--
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