On Tue, 14 Jun 2011 12:04:12 +0200
Johannes Weiner [off-list ref] wrote:

On Mon, Jun 13, 2011 at 12:16:48PM +0900, KAMEZAWA Hiroyuki wrote:

quoted

@@ -1670,8 +1670,8 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 		victim = mem_cgroup_select_victim(root_mem);
 		if (victim == root_mem) {
 			loop++;
-			if (loop >= 1)
-				drain_all_stock_async();
+			if (!check_soft && loop >= 1)
+				drain_all_stock_async(root_mem);

I agree with Michal, this should be a separate change.

Hm, ok, I'll do.

quoted

@@ -2008,26 +2011,50 @@ static void refill_stock(struct mem_cgroup *mem, unsigned int nr_pages)
  * expects some charges will be back to res_counter later but cannot wait for
  * it.
  */
-static void drain_all_stock_async(void)
+static void drain_all_stock_async(struct mem_cgroup *root_mem)
 {
-	int cpu;
-	/* This function is for scheduling "drain" in asynchronous way.
-	 * The result of "drain" is not directly handled by callers. Then,
-	 * if someone is calling drain, we don't have to call drain more.
-	 * Anyway, WORK_STRUCT_PENDING check in queue_work_on() will catch if
-	 * there is a race. We just do loose check here.
+	int cpu, curcpu;
+	/*
+	 * If someone calls draining, avoid adding more kworker runs.
 	 */
-	if (atomic_read(&memcg_drain_count))
+	if (!mutex_trylock(&percpu_charge_mutex))
 		return;
 	/* Notify other cpus that system-wide "drain" is running */
-	atomic_inc(&memcg_drain_count);
 	get_online_cpus();
+
+	/*
+	 * get a hint for avoiding draining charges on the current cpu,
+	 * which must be exhausted by our charging. But this is not
+	 * required to be a precise check, We use raw_smp_processor_id()
+	 * instead of getcpu()/putcpu().
+	 */
+	curcpu = raw_smp_processor_id();
 	for_each_online_cpu(cpu) {
 		struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
-		schedule_work_on(cpu, &stock->work);
+		struct mem_cgroup *mem;
+
+		if (cpu == curcpu)
+			continue;
+
+		mem = stock->cached;
+		if (!mem)
+			continue;
+		if (mem != root_mem) {
+			if (!root_mem->use_hierarchy)
+				continue;
+			/* check whether "mem" is under tree of "root_mem" */
+			rcu_read_lock();
+			if (!css_is_ancestor(&mem->css, &root_mem->css)) {
+				rcu_read_unlock();
+				continue;
+			}
+			rcu_read_unlock();

css_is_ancestor() takes the rcu read lock itself already.

you're right.

I'll post an update.

Thanks,
-Kame

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