[Devel] Re: [Fwd: [PATCH -RSS 2/2] Fix limit check after reclaim]

[Pavel Emelianov]

Balbir Singh wrote:
> Pavel Emelianov wrote:
>>> +static inline bool res_counter_check_under_limit(struct res_counter *cnt)
>>> +{
>>> +	bool ret;
>>> +	unsigned long flags;
>>> +
>>> +	spin_lock_irqsave(&cnt->lock, flags);
>>> +	ret = res_counter_limit_check_locked(cnt);
>> We don't have to take the lock for such a check.
>>
>  
> This check without the lock could be racy and return incorrect
> results -- leading to OOM.

Maybe. Nevertheless, if we do not trust the return value of
try_to_free_pages() then the code should probably look like

while (1) {
	if (res_counter_charge() == 0)
		break;

	did_progress = try_to_free_pages();
	if (res_counter_charge() == 0)
		break;

	if (!did_progress)
		out_of_memory();
}

But in any case we must know for sure was at least one page
freed or not...

Thanks,
Pavel