linux-kernel - Re: [PATCH 1/1] mm: only dispaly online cpus of the numa node

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Date:   Fri, 29 Sep 2017 14:46:49 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>, Will Deacon <will.deacon@....com>
CC:     linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm <linux-mm@...ck.org>, Zefan Li <lizefan@...wei.com>,
        Xinwei Hu <huxinwei@...wei.com>,
        Tianhong Ding <dingtianhong@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH 1/1] mm: only dispaly online cpus of the numa node



On 2017/8/28 21:13, Michal Hocko wrote:
> On Fri 25-08-17 18:34:33, Will Deacon wrote:
>> On Thu, Aug 24, 2017 at 10:32:26AM +0200, Michal Hocko wrote:
>>> It seems this has slipped through cracks. Let's CC arm64 guys
>>>
>>> On Tue 20-06-17 20:43:28, Zhen Lei wrote:
>>>> When I executed numactl -H(which read /sys/devices/system/node/nodeX/cpumap
>>>> and display cpumask_of_node for each node), but I got different result on
>>>> X86 and arm64. For each numa node, the former only displayed online CPUs,
>>>> and the latter displayed all possible CPUs. Unfortunately, both Linux
>>>> documentation and numactl manual have not described it clear.
>>>>
>>>> I sent a mail to ask for help, and Michal Hocko <mhocko@...nel.org> replied
>>>> that he preferred to print online cpus because it doesn't really make much
>>>> sense to bind anything on offline nodes.
>>>
>>> Yes printing offline CPUs is just confusing and more so when the
>>> behavior is not consistent over architectures. I believe that x86
>>> behavior is the more appropriate one because it is more logical to dump
>>> the NUMA topology and use it for affinity setting than adding one
>>> additional step to check the cpu state to achieve the same.
>>>
>>> It is true that the online/offline state might change at any time so the
>>> above might be tricky on its own but if we should at least make the
>>> behavior consistent.
>>>
>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>>>
>>> Acked-by: Michal Hocko <mhocko@...e.com>
>>
>> The concept looks find to me, but shouldn't we use cpumask_var_t and
>> alloc/free_cpumask_var?
> 
> This will be safer but both callers of node_read_cpumap are shallow
> stack so I am not sure a stack is a limiting factor here.
> 
> Zhen Lei, would you care to update that part please?
> 
Sure, I will send v2 immediately.

I'm so sorry that missed this email until someone told me.

-- 
Thanks!
BestRegards