[PATCH V6 09/10] Add API to export per-memcg kswapd pid.

[Ying Han <yinghan@google.com>]

This add the API which exports per-memcg kswapd thread pid. The kswapd
thread is named as "memcg_" + css_id, and the pid can be used to put
kswapd thread into cpu cgroup later.

$ mkdir /dev/cgroup/memory/A
$ cat /dev/cgroup/memory/A/memory.kswapd_pid
memcg_null 0

$ echo 500m >/dev/cgroup/memory/A/memory.limit_in_bytes
$ echo 50m >/dev/cgroup/memory/A/memory.high_wmark_distance
$ ps -ef | grep memcg
root      6727     2  0 14:32 ?        00:00:00 [memcg_3]
root      6729  6044  0 14:32 ttyS0    00:00:00 grep memcg

$ cat memory.kswapd_pid
memcg_3 6727

changelog v6..v5
1. Remove the legacy spinlock which has been removed from previous post.

changelog v5..v4
1. Initialize the memcg-kswapd pid to -1 instead of 0.
2. Remove the kswapds_spinlock.

changelog v4..v3
1. Add the API based on KAMAZAWA's request on patch v3.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Ying Han <yinghan@google.com>
---
 mm/memcontrol.c |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d5b284c..0b108b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4533,6 +4533,33 @@ static int mem_cgroup_wmark_read(struct cgroup *cgrp,
 	return 0;
 }
 
+static int mem_cgroup_kswapd_pid_read(struct cgroup *cgrp,
+	struct cftype *cft,  struct cgroup_map_cb *cb)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
+	struct task_struct *kswapd_thr = NULL;
+	struct kswapd *kswapd_p = NULL;
+	wait_queue_head_t *wait;
+	char name[TASK_COMM_LEN];
+	pid_t pid = -1;
+
+	sprintf(name, "memcg_null");
+
+	wait = mem_cgroup_kswapd_wait(mem);
+	if (wait) {
+		kswapd_p = container_of(wait, struct kswapd, kswapd_wait);
+		kswapd_thr = kswapd_p->kswapd_task;
+		if (kswapd_thr) {
+			get_task_comm(name, kswapd_thr);
+			pid = kswapd_thr->pid;
+		}
+	}
+
+	cb->fill(cb, name, pid);
+
+	return 0;
+}
+
 static int mem_cgroup_oom_control_read(struct cgroup *cgrp,
 	struct cftype *cft,  struct cgroup_map_cb *cb)
 {
@@ -4650,6 +4677,10 @@ static struct cftype mem_cgroup_files[] = {
 		.name = "reclaim_wmarks",
 		.read_map = mem_cgroup_wmark_read,
 	},
+	{
+		.name = "kswapd_pid",
+		.read_map = mem_cgroup_kswapd_pid_read,
+	},
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
-- 
1.7.3.1

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