linux-kernel - Re: [PATCH] nvme: allow ANA support to be independent of native multipathing

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Date:   Fri, 16 Nov 2018 11:06:32 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Mike Snitzer <snitzer@...hat.com>, linux-nvme@...ts.infradead.org,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>, axboe@...nel.dk,
        Martin Wilck <mwilck@...e.com>, lijie <lijie34@...wei.com>,
        xose.vazquez@...il.com, chengjike.cheng@...wei.com,
        shenhong09@...wei.com, dm-devel@...hat.com,
        wangzhoumengjian@...wei.com, christophe.varoqui@...nsvc.com,
        bmarzins@...hat.com, sschremm@...app.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: allow ANA support to be independent of native
 multipathing

On 11/16/18 10:49 AM, Christoph Hellwig wrote:
> On Fri, Nov 16, 2018 at 10:40:40AM +0100, Hannes Reinecke wrote:
>>>> Introduce ability to always re-read ANA log page as required due to ANA
>>>> error and make current ANA state available via sysfs -- even if native
>>>> multipathing is disabled on the host (e.g. nvme_core.multipath=N).
>>>
>>> The first part I could see, but I still want to make it conditional
>>> in some way as nvme is going into deeply embedded setups, and I don't
>>> want to carry the weight of the ANA code around for everyone.
>>>
>> Can you clarify this a bit?
>> We _do_ have the NVME multipath config option to deconfigure the whole
>> thing during compile time; that isn't influenced with this patch.
>> So are you worried about the size of the ANA implementation itself?
>> Or are you worried about the size of the ANA structures?
> 
> I just see the next step of wanting to move ANA code into the core
> which is implied above.

Really, I couldn't care less _where_ the ANA code lives.
If the size of which is any concern we can even make it configurable of 
sorts.

>>
>>> The second I fundamentally disagree with.  And even if you found agreement
>>> it would have to be in a separate patch as it is a separate feature.
>>>
>> Why? Where's the problem with re-reading the ANA log pages if we get an
>> event indicating that we should?
> 
> "second" here means the sysfs file.
> 
Ok, so would you be happy with making ANA support configurable?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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