alinux: mm, memcg: account number of processes in the css

Since commit e0205ae40f12 ("mm: memcontrol: use CSS_TASK_ITER_PROCS at
mem_cgroup_scan_tasks()") made mem_cgroup_scan_tasks() to check only one
thread from each thread group, we can make cgroup_subsys_state::nr_tasks
to record only the thread group leader, i.e., process, instead of
thread(s). Furthermore, this renames cgroup_subsys_state::nr_tasks to
cgroup_subsys_state::nr_procs.

Fixes: f061cd88 ("alinux: kernel: cgroup: account number of tasks in
the css and its descendants")
Signed-off-by: NXu Yu <xuyu@linux.alibaba.com>
Reviewed-by: NYang Shi <yang.shi@linux.alibaba.com>
Reviewed-by: NXunlei Pang <xlpang@linux.alibaba.com>

include/linux/cgroup-defs.h

@@ -141,8 +141,8 @@ struct cgroup_subsys_state {
 	 */
 	int id;
 
-	/* number of tasks under this css and its descendants */
-	int nr_tasks;
+	/* number of procs under this css and its descendants */
+	int nr_procs;
 
 	unsigned int flags;
 

kernel/cgroup/cgroup.c

@@ -1796,20 +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)
+static void css_account_procs(struct task_struct *task,
+			      struct css_set *cset, int num)
 {
 	struct cgroup_subsys *ss;
 	int ssid;
 
+	if (!thread_group_leader(task))
+		return;
+
 	for_each_subsys(ss, ssid) {
 		struct cgroup_subsys_state *css = cset->subsys[ssid];
 
 		if (!css)
 			continue;
-		css->nr_tasks += num;
+		css->nr_procs += num;
 		while (css->parent) {
 			css = css->parent;
-			css->nr_tasks += num;
+			css->nr_procs += num;
 		}
 	}
 }
@@ -1865,7 +1869,7 @@ 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);
+			css_account_procs(p, cset, 1);
 		}
 		spin_unlock(&p->sighand->siglock);
 	} while_each_thread(g, p);
@@ -2358,11 +2362,11 @@ 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_account_procs(task, 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);
+			css_account_procs(task, from_cset, -1);
 		}
 	}
 	spin_unlock_irq(&css_set_lock);
@@ -5849,7 +5853,7 @@ 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_account_procs(child, cset, 1);
 			css_set_move_task(child, NULL, cset, false);
 		}
 		spin_unlock_irq(&css_set_lock);
@@ -5901,7 +5905,7 @@ 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);
+		css_account_procs(tsk, cset, -1);
 		spin_unlock_irq(&css_set_lock);
 	} else {
 		get_css_set(cset);

mm/memcontrol.c

@@ -1158,7 +1158,7 @@ mem_cgroup_select_victim_cgroup(struct mem_cgroup *memcg)
 
 		parent_mem = mem_cgroup_from_css(parent);
 
-		if (parent->nr_tasks <= parent_mem->num_oom_skip)
+		if (parent->nr_procs <= parent_mem->num_oom_skip)
 			break;
 		victim = parent;
 		chosen = NULL;
@@ -1168,7 +1168,7 @@ mem_cgroup_select_victim_cgroup(struct mem_cgroup *memcg)
 
 			tmp = mem_cgroup_from_css(pos);
 
-			if (pos->nr_tasks <= tmp->num_oom_skip)
+			if (pos->nr_procs <= tmp->num_oom_skip)
 				continue;
 			if (tmp->priority > chosen_priority)
 				continue;