From f061cd8828eb0d1e2d19ceedf3146844445aa1b6 Mon Sep 17 00:00:00 2001
From: Wenwei Tao <wenwei.tao@linux.alibaba.com>
Date: Mon, 26 Aug 2019 15:18:30 +0800
Subject: [PATCH] alinux: kernel: cgroup: account number of tasks in the css
 and its descendants

Account number of the tasks in the css and its descendants, this is
prepared for the incoming memcg priority patch.

In memcg priority oom, we will select victim cgroup which has victim
tasks in it. We need to know whether the memcg and its descendants
have tasks before the selection can move on.

Signed-off-by: Wenwei Tao <wenwei.tao@linux.alibaba.com>
Reviewed-by: Xunlei Pang <xlpang@linux.alibaba.com>
---
 include/linux/cgroup-defs.h |  3 +++
 kernel/cgroup/cgroup.c      | 23 +++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 15261d74baa4..6f0766ea159b 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -141,6 +141,9 @@ struct cgroup_subsys_state {
 	 */
 	int id;
 
+	/* number of tasks under this css and its descendants */
+	int nr_tasks;
+
 	unsigned int flags;
 
 	/*
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 474a23b15822..237080ee3305 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1796,6 +1796,24 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
 	return 0;
 }
 
+static void css_account_tasks(struct css_set *cset, int num)
+{
+	struct cgroup_subsys *ss;
+	int ssid;
+
+	for_each_subsys(ss, ssid) {
+		struct cgroup_subsys_state *css = cset->subsys[ssid];
+
+		if (!css)
+			continue;
+		css->nr_tasks += num;
+		while (css->parent) {
+			css = css->parent;
+			css->nr_tasks += num;
+		}
+	}
+}
+
 /*
  * To reduce the fork() overhead for systems that are not actually using
  * their cgroups capability, we don't maintain the lists running through
@@ -1847,6 +1865,7 @@ static void cgroup_enable_task_cg_lists(void)
 			list_add_tail(&p->cg_list, &cset->tasks);
 			get_css_set(cset);
 			cset->nr_tasks++;
+			css_account_tasks(cset, 1);
 		}
 		spin_unlock(&p->sighand->siglock);
 	} while_each_thread(g, p);
@@ -2339,9 +2358,11 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)
 
 			get_css_set(to_cset);
 			to_cset->nr_tasks++;
+			css_account_tasks(to_cset, 1);
 			css_set_move_task(task, from_cset, to_cset, true);
 			put_css_set_locked(from_cset);
 			from_cset->nr_tasks--;
+			css_account_tasks(from_cset, -1);
 		}
 	}
 	spin_unlock_irq(&css_set_lock);
@@ -5828,6 +5849,7 @@ void cgroup_post_fork(struct task_struct *child)
 		if (list_empty(&child->cg_list)) {
 			get_css_set(cset);
 			cset->nr_tasks++;
+			css_account_tasks(cset, 1);
 			css_set_move_task(child, NULL, cset, false);
 		}
 		spin_unlock_irq(&css_set_lock);
@@ -5879,6 +5901,7 @@ void cgroup_exit(struct task_struct *tsk)
 		css_set_move_task(tsk, cset, NULL, false);
 		list_add_tail(&tsk->cg_list, &cset->dying_tasks);
 		cset->nr_tasks--;
+		css_account_tasks(cset, -1);
 		spin_unlock_irq(&css_set_lock);
 	} else {
 		get_css_set(cset);
-- 
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