Re: [PATCH] rudimentary tracing for Classic RCU

[Lai Jiangshan]

KOSAKI Motohiro wrote:
> Hi Lai-san,
> 
>>>> In this case, why not define it as:
>>>> static char buf[20*NR_CPUS + 100];
>>> Actually you should near never use NR_CPUS now but always num_possible_cpus()
>>> (or even num_online_cpus()) Using NR_CPUS can lead to extreme waste
>>> of memory on kernels which are compiled for 4096 CPUs for example.
>>>
>>> And with num_possible_cpus() kmalloc is needed.
>> I thought the default value of NR_CPUS is 32.
> 
> it's pointless.
> Almost distribution use _very_ large NR_CPUS (likes 4096).
> So, We should concern large NR_CPUS.

Thanks.

So my advice is to use seq_file.

> 
> 
>> if NR_CPUS is too large, I think using seq_file is good idea,
>> and rcuclassic_trace_mutex is not need too.
> 
> 
> 
> 
> 


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