Re: [PATCH v4 1/3] block: Improve checks on zone resource limits

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On 6/6/24 10:21 AM, Niklas Cassel wrote:
>> Right now, this all works the same way for DM and nvme zns, so I think this is
>> all good. If anything, we should probably add a warning in the nvme driver
>> about the potentially unreliable moz/moz limits if we see a ZNS device with
>> multiple zoned namespaces.
> 
> Well, it is only a problem for ZNS devices with NS management.
> 
> If there are two ZNS namespaces on the device, and the device does not
> support NS management, the device vendor would have been seriously silly
> to not allocate and set the limits in the I/O Command Set Specific Identify
> Namespace Data Structure for the Zoned Namespace Command Set correctly.
> 
> But yes, this concern cannot be solved in disk_update_zone_resources(),
> which operates on per gendisk (and there is one gendisk per namespace),
> so not much this function can do. If we were to do something, it would
> have to be done in the nvme driver.
> 
> 
> Perhaps if the device is ZNS, and does support NS management, but does
> not have the Zoned Namespace Resource Management supported bit is set,
> divide the MAR/MOR values reported by each namespace by the number of
> ZNS namespaces?

Maybe. But that would still not provide any guarantee: a buggy application not
respecting the limits would be able to steal resources from the other namespace.

In any case, I think this is a discussion to have on the nvme list.

-- 
Damien Le Moal
Western Digital Research





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