Re: [RFC] memory controller : backgorund reclaim and avoid excessive locking [4/5] borrow resource

[yamamoto-jCdQPDEk3idL9jVzuh4AOg@public.gmane.org (YAMAMOTO Takashi)]

> +		/* try to charge */
> +		ret = res_counter_charge(&mem->res, mem->borrow_unit);
> +		if (!ret) { /* success */
> +			*bwp += (mem->borrow_unit - size);
> +			goto out;
> +		}
> +	}
> +	spin_lock(&mem->res.lock);
> +	ret = res_counter_charge_locked(&mem->res, size);
> +	spin_unlock(&mem->res.lock);

although i don't know if it matters, this retrying of charge affects failcnt.

> +static void mem_cgroup_return_and_uncharge(struct mem_cgroup *mem, int size)
> +{
> +	unsigned long flags;
> +	int uncharge_size = 0;
> +
> +	local_irq_save(flags);
> +	if (mem->borrow_unit) {
> +		int limit = mem->borrow_unit * 2;
> +		int cpu;
> +		s64 *bwp;
> +		cpu = smp_processor_id();
> +		bwp = &mem->stat.cpustat[cpu].count[MEM_CGROUP_STAT_BORROW];
> +		*bwp += size;
> +		if (*bwp > limit) {
> +			uncharge_size = *bwp - mem->borrow_unit;
> +			*bwp = mem->borrow_unit;
> +		}
> +	} else
> +		uncharge_size = size;
> +
> +	if (uncharge_size) {
> +		spin_lock(&mem->res.lock);
> +		res_counter_uncharge_locked(&mem->res, size);

s/size/uncharge_size/

> @@ -1109,12 +1202,29 @@ static u64 mem_throttle_read(struct cgro
>  	return (u64)mem->throttle.limit;
>  }
>  
> +static int mem_bulkratio_write(struct cgroup *cont, struct cftype *cft, u64 val)
> +{
> +	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> +	int unit = val * PAGE_SIZE;
> +	if (unit > (PAGE_SIZE << (MAX_ORDER/2)))
> +		return -EINVAL;
> +	mem->borrow_unit = unit;
> +	return 0;
> +}

it seems unsafe with concurrent mem_cgroup_borrow_and_charge or
mem_cgroup_return_and_uncharge.

YAMAMOTO Takashi