[PATCH] nvme-multipath: add an 'ana_groups_only' module option

[Hannes Reinecke]

On 2/9/22 09:07, Christoph Hellwig wrote:
> On Mon, Feb 07, 2022 at 11:00:05AM +0100, Hannes Reinecke wrote:
>> On large installations the ANA log buffer can be exceedingly large;
>> we've come across a controller with 49 ANA Group Descriptors and
>> 65536 namespaces, resulting in an ANA buffer with an order-7 allocation.
>> And this is just to validate that the namespace ID is _really_listed
>> in the log page.
>> So to avoid an overly large memory allocation we can leverage the
>> 'RGO' bit when retrieving the ANA log page, and check whether the
>> ANA group ID from the namespace is found in the ANA descriptors.
>> That cuts down the memory allocation, and provides the same result.
>> But to be on the safe side I've added a module option 'ana_groups_only'
>> to switch between modes.
> 
> How is this supposed to work?  We'll fail to see what namespaces
> the change applies to.
> 
How so?
I'm just reverting the check; instead of having the nsid listed in the 
ana log page and check for a match between the nsids we now check for a 
match between the group id in the ana log page and the ana grpid from 
the 'identify namespace' output.
So I'm still able to identify which namespace this change belongs to.

> So in doubt fix the controller config to be less broken (and say hello
> to NetApp and explain them they do not need more namespace for more
> performance), and if that fails switch to a vmalloc allocation for
> the buffer.

Curiously it was _not_ NetApp, but I'll happily explain this to the 
reporters :-)

But I'll have a look a vmalloc anyway.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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