Re: [PATCH] memcg: Free spare array to avoid memory leak

[Sha Zhengju <handai.szj-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 03/08/2012 06:35 PM, Kirill A. Shutemov wrote:
> On Thu, Mar 08, 2012 at 10:11:32AM +0800, Sha Zhengju wrote:
>> On 03/08/2012 07:08 AM, Kirill A. Shutemov wrote:
>>> On Tue, Mar 06, 2012 at 08:13:24PM +0800, Sha Zhengju wrote:
>>>> From: Sha Zhengju<handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
>>>>
>>>> When the last event is unregistered, there is no need to keep the spare
>>>> array anymore. So free it to avoid memory leak.
>>> It's not a leak. It will be freed on next event register.
>>
>> Yeah, I noticed that. But what if it is just the last one and no more
>> event registering ?
> See my question below. ;)
>
>>> Yeah, we don't have to keep spare if primary is empty. But is it worth to
>>> make code more complicated to save few bytes of memory?
>>>
If we unregister the last event and *don't* register a new event anymore,
the primary is freed but the spare is still kept which has no chance to
free.

IMHO, it's obvious not a problem of saving bytes but *memory leak*.

>>>> Signed-off-by: Sha Zhengju<handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
>>>>
>>>> ---
>>>>   mm/memcontrol.c |    6 ++++++
>>>>   1 files changed, 6 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>>> index 22d94f5..3c09a84 100644
>>>> --- a/mm/memcontrol.c
>>>> +++ b/mm/memcontrol.c
>>>> @@ -4412,6 +4412,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
>>>>   swap_buffers:
>>>>   	/* Swap primary and spare array */
>>>>   	thresholds->spare = thresholds->primary;
>>>> +	/* If all events are unregistered, free the spare array */
>>>> +	if (!new) {
>>>> +		kfree(thresholds->spare);
>>>> +		thresholds->spare = NULL;
>>>> +	}
>>>> +
>>>>   	rcu_assign_pointer(thresholds->primary, new);
>>>>
>>>>   	/* To be sure that nobody uses thresholds */
>>>> -- 
>>>> 1.7.4.1
>>>>