Re: [dpdk-stable] [PATCH] mem: fix allocation failure on non-NUMA kernel

[Nick Connolly <nick.connolly@mayadata.io>]

Excellent - thanks - I'll amend the patch.

On 17/09/2020 15:07, Burakov, Anatoly wrote:
> On 17-Sep-20 2:05 PM, Nick Connolly wrote:
>> Hi Anatoly,
>>
>> Thanks.  My recollection is that all of the NUMA configuration flags 
>> were set to 'n'.
>>
>> Regards,
>> Nick
>>
>> On 17/09/2020 13:57, Burakov, Anatoly wrote:
>>> On 17-Sep-20 1:29 PM, Nick Connolly wrote:
>>>> Hi Anatoly,
>>>>
>>>> Thanks for the response.  You are asking a good question - here's 
>>>> what I know:
>>>>
>>>> The issue arose on a single socket system, running WSL2 (full Linux 
>>>> kernel running as a lightweight VM under Windows).
>>>> The default kernel in this environment is built with CONFIG_NUMA=n 
>>>> which means get_mempolicy() returns an error.
>>>> This causes the check to ensure that the allocated memory is 
>>>> associated with the correct socket to fail.
>>>>
>>>> The change is to skip the allocation check if check_numa() 
>>>> indicates that NUMA-aware memory is not supported.
>>>>
>>>> Researching the meaning of CONFIG_NUMA, I found 
>>>> https://cateee.net/lkddb/web-lkddb/NUMA.html which says:
>>>>> Enable NUMA (Non-Uniform Memory Access) support.
>>>>> The kernel will try to allocate memory used by a CPU on the local 
>>>>> memory controller of the CPU and add some more NUMA awareness to 
>>>>> the kernel.
>>>>
>>>> Clearly CONFIG_NUMA enables memory awareness, but there's no 
>>>> indication in the description whether information about the NUMA 
>>>> physical architecture is 'hidden', or whether it is still exposed 
>>>> through /sys/devices/system/node* (which is used by the rte 
>>>> initialisation code to determine how many sockets there are). 
>>>> Unfortunately, I don't have ready access to a multi-socket Linux 
>>>> system that I can test this out on, so I took the conservative 
>>>> approach that it may be possible to have CONFIG_NUMA disabled, but 
>>>> the kernel still report more than one node, and coded the change to 
>>>> generate a debug message if this occurs.
>>>>
>>>> Do you know whether CONFIG_NUMA turns off all knowledge about the 
>>>> hardware architecture?  If it does, then I agree that the test for 
>>>> rte_socket_count() serves no purpose and should be removed.
>>>>
>>>
>>> I have a system with a custom compiled kernel, i can recompile it 
>>> without this flag and test this. I'll report back with results :)
>>>
>>
>
> With CONFIG_NUMA set to 'n':
>
> [root@xxx ~]# find /sys -name "node*"
> /sys/kernel/software_nodes/node0
> [root@xxx ~]#
>
> This is confirmed by running DPDK on that machine - i can see all 
> cores from all sockets, but they're all appearing on socket 0. So, 
> yes, that check isn't necessary :)
>