Re: [BUGFIX][PATCH 5/5] memcg: fix percpu cached charge draining frequency

Johannes Weiner
2011-06-14T10:05:05Z

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

> @@ -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.