Re: [PATCH 3/3] nfnetlink_queue: use hash table to speed up entry finding.

[Patrick McHardy <kaber@trash.net>]

Patrick McHardy wrote:
> Changli Gao wrote:
>> On Thu, Apr 15, 2010 at 6:36 PM, Patrick McHardy <kaber@trash.net> wrote:
>>> Changli Gao wrote:
>>>> On Tue, Apr 13, 2010 at 9:25 PM, Patrick McHardy <kaber@trash.net> wrote:
>>>>>> Yes, that is why vmalloc() is perfect for this case. No extra memory for
>>>>>> management, but one pointer for each page of memory.
>>>>> I agree, if it works for conntrack, it certainly also works for
>>>>> nfnetlink_queue.
>>>>>
>>>> I need to allocate memory in atomic section, so vmalloc() can't be used. :(
>>> Why?
>>>
>> instance_create() is called in rcu read-side critical section, and the
>> whole body of this function is protected by the spinlock
>> instances_lock. All these make memory allocation for queue instances
>> should be atomic.
> 
> That should be easily fixable. For the lookup we can add a reference
> counter so we don't need the rcu read side critical section.

Actually we don't even need that, since we're holding nfnl_mutex the
instance can't go away.

> For creation the lock actually looks unnecessary since all nfnetlink
> handlers run under nfnl_mutex, so we can't have concurrent creation
> and removal of queuing instances. Well, we need it for list insertion
> to avoid races with the seq file handlers, but we don't need it
> before that.