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

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Message-ID: <1542396866.13202.0.camel@redhat.com>
Date:   Fri, 16 Nov 2018 14:34:26 -0500
From:   Laurence Oberman <loberman@...hat.com>
To:     Mike Snitzer <snitzer@...hat.com>, Christoph Hellwig <hch@....de>
Cc:     Hannes Reinecke <hare@...e.de>, 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: nvme: allow ANA support to be independent of native multipathing

On Fri, 2018-11-16 at 14:28 -0500, Mike Snitzer wrote:
> On Fri, Nov 16 2018 at  5:17am -0500,
> Christoph Hellwig <hch@....de> wrote:
> 
> > On Fri, Nov 16, 2018 at 11:06:32AM +0100, Hannes Reinecke wrote:
> > > Ok, so would you be happy with making ANA support configurable?
> > 
> > I've looked a bit over the whole situation, and what I think we
> > need
> > to do is:
> > 
> >  a) warn if we see a ANA capable device without multipath support
> >     so people know it is not going to work properly.
> 
> I disagree with your cynicism but v2 of this patch now emits a
> warning
> accordingly.
> 
> >  b) deprecate the multipath module option.  It was only intended as
> >     a migration for any pre-existing PCIe multipath user if there
> >     were any, not to support any new functionality.  So for 4.20
> >     put in a patch that prints a clear warning when it is used,
> >     including a link to the nvme list, and then for 4.25 or so
> >     remove it entirely unless something unexpected come up.
> 
> You rejected the idea of allowing fine-grained control over whether
> native NVMe multipathing is enabled or not on a per-namespace basis.
> All we have is the coarse-grained nvme_core.multipath=N knob.  Now
> you're forecasting removing even that.  Please don't do that.
> 
> > This whole drama of optional multipath use has wasted way too much
> > of everyones time already.
> 
> It has wasted _way_ too much time.
> 
> But the drama is born out of you rejecting that we need to preserve
> multipath-tools and dm-multipath's ability to work across any
> transport.  You don't need to do that work: Hannes, myself and others
> have always been willing and able -- if you'd let us.
> 
> IIRC it was at 2016's LSF in Boston where Ewan Milne and I had a
> face-to-face conversation with you in the hallway track where you
> agreed
> that ANA support would be activated if the capability was advertised
> by
> the target.  The model we discussed is that it would be comparable to
> how ALUA gets enabled during SCSI LUN discovery.
> 
> I hope you can see your way forward to be more accommodating now.
> Especially given the proposed changes are backed by NVMe standards.
> 
> Please, PLEASE take v2 of this patch.. please? ;)
> 
> Thanks,
> Mike

I am begging you take it too please 
Thanks
Laurence