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

[Nick Connolly]

Hi Nicolas,

Thanks for the quick response.

On 05/08/2020 14:42, Nicolas Dichtel wrote:
> Le 05/08/2020 à 14:26, Nick Connolly a écrit :
>> Running dpdk-helloworld on Linux with lib numa present,
>> but no kernel support for NUMA (CONFIG_NUMA=n) causes
>> ret_service_init() to fail with EAL: error allocating
>> rte services array.
>>
>> alloc_seg() calls get_mempolicy to verify that the allocation
>> has happened on the correct socket, but receives ENOSYS from
>> the kernel and fails the allocation.
>>
>> The allocated socket should only be verified if check_numa() is true.
>>
>> Fixes: 2a96c88be83e ("mem: ease init in a docker container")
> I'm wondering if the bug existed before this commit.
>
> Before this commit, it was:
>         move_pages(getpid(), 1, &addr, NULL, &cur_socket_id, 0);
>         if (cur_socket_id != socket_id) {
>                 /* error */
>
> Isn't it possible to hit this error case if CONFIG_NUMA is unset in the kernel?
I've just run the previous code to test this out and you are right that 
move_pages does indeed return -1 with errno set to ENOSYS, but nothing 
checks this so execution carries on and compares cur_socket_id (which 
will be unchanged from the zero initialization) with socket_id (which is 
presumably also zero), thus allowing the allocation to succeed!

> [snip]
>> +	if (check_numa()) {
>> +		ret = get_mempolicy(&cur_socket_id, NULL, 0, addr,
>> +					MPOL_F_NODE | MPOL_F_ADDR);
>> +		if (ret < 0) {
>> +			RTE_LOG(DEBUG, EAL, "%s(): get_mempolicy: %s\n",
>> +				__func__, strerror(errno));
>> +			goto mapped;
>> +		} else if (cur_socket_id != socket_id) {
>> +			RTE_LOG(DEBUG, EAL,
>> +					"%s(): allocation happened on wrong socket (wanted %d, got %d)\n",
>> +				__func__, socket_id, cur_socket_id);
>> +			goto mapped;
>> +		}
>> +	} else {
>> +		if (rte_socket_count() > 1)
>> +			RTE_LOG(DEBUG, EAL, "%s(): not checking socket for allocation (wanted %d)\n",
>> +					__func__, socket_id);
> nit: maybe an higher log level like WARNING?
Open to guidance here - my concern was that this is going to be 
generated for every call to alloc_seg() and I'm not sure what the 
frequency will be - I'm cautious about flooding the log with warnings 
under 'normal running'.  Are the implications of running on a multi 
socket system with NUMA support disabled in the kernel purely 
performance related for the DPDK or is there a functional correctness 
issue as well?
>
> Regards,
> Nicolas

Regards,
Nick