Re: [RCU problem] was VFS: file-max limit 50044 reached

[Eric Dumazet <dada1@cosmosbay.com>]

Dipankar Sarma a écrit :
> On Mon, Oct 17, 2005 at 02:10:09PM +0200, Eric Dumazet wrote:
> 
>>Dipankar Sarma a écrit :
>>
>>>On Mon, Oct 17, 2005 at 11:10:04AM +0200, Eric Dumazet wrote:
>>>
>>>Agreed. It is not designed to work that way, so there must be
>>>a bug somewhere and I am trying to track it down. It could very well
>>>be that at maxbatch=10 we are just queueing at a rate far too high
>>>compared to processing.
>>>
>>
>>I can freeze my test machine with a program that 'only' use dentries, no 
>>files.
>>
>>No message, no panic, but machine becomes totally unresponsive after few 
>>seconds.
>>
>>Just greping for call_rcu in kernel sources gave me another call_rcu() use 
>>from syscalls. And yes 2.6.13 has the same problem.
> 
> 
> Can you try it with rcupdate.maxbatch set to 10000 in boot
> command line ?
> 

Changing maxbatch from 10 to 10000 cures the problem.
Maybe we could initialize maxbatch to (10000000/HZ), considering no current 
cpu is able to queue more than 10.000.000 items per second in a list.


> FWIW, the open/close test problem goes away if I set maxbatch to
> 10000. I had introduced this limit some time ago to curtail
> the effect long running softirq handlers have on scheduling
> latencies, which now conflicts with OOM avoidance requirements.

Yes, and probably OOM avoidance has a higher priority than latencies in DOS 
situations...

Eric