[dpdk-dev] The limitation of VHOST_MEMORY_MAX_NREGIONS in virtio-user with vhost-user backend

[Maxime Coquelin]

On 12/06/2017 03:06 PM, Yuanhan Liu wrote:
> On Wed, Dec 06, 2017 at 12:23:19PM +0100, Maxime Coquelin wrote:
>> Hi,
>>
>> On 12/05/2017 07:58 AM, Wang, Wei 5. (NSB - CN/Hangzhou) wrote:
>>>
>>>
>>> Hi, all
>>>
>>> In DPDK document, it it described that Virtio in containers Cannot work when there are more than VHOST_MEMORY_MAX_NREGIONS(8) hugepages. In another word, do not use 2MB hugepage so far. Do you know the reason of this limitation?
>>
>> What document are you referring to?
>> Actually, a single region is composed of several hugepages, be it 1G or
>> 2M. I use 2M hugepages daily without issues.
> 
> He was talking about virtio-user.

Ok, thanks for the correction.

The lookup time for every translation will be very costly if we have one
region per 2MB page.

> 
> 	--yliu
>>
>> The limitation comes from the Vhost-user protocol spec. I know there are
>> discussions to enlarge it, but it would require a new protocol flag not
>> to break existing implementations, so no workaround possible.
>>
>>> In my envirionment, the pdpe1gb is not set in cpu flag, so hugepage can't be set to 1GB size. The hugepage number shall be more than 8
>>>
>>>
>>> So is there any solution or workaround to fix this limitation? Or change dpdk code to fix this limitation?
>>
>> Have you tried to use 2MB pages and faced the NREGIONS > 8 case?
>> If so, could you tell us more about your setup (QEMU version, VM RAM
>> size, etc...)?
>>
>> Cheers,
>> Maxime
>>>
>>>
>>> Vivian
>>> seat:      19009
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>>>
>>>
>>>