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Date:   Tue, 6 Oct 2020 20:18:14 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Olga Kornievskaia <aglo@umich.edu>
Cc:     Benjamin Coddington <bcodding@redhat.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
Subject: Re: unsharing tcp connections from different NFS mounts
Message-ID: <20201007001814.GA5138@fieldses.org>
References: <20201006151335.GB28306@fieldses.org>
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On Tue, Oct 06, 2020 at 05:46:11PM -0400, Olga Kornievskaia wrote:
> On Tue, Oct 6, 2020 at 3:38 PM Benjamin Coddington <bcodding@redhat.com> wrote:
> >
> > On 6 Oct 2020, at 11:13, J. Bruce Fields wrote:
> >
> > > NFSv4.1+ differs from earlier versions in that it always performs
> > > trunking discovery that results in mounts to the same server sharing a
> > > TCP connection.
> > >
> > > It turns out this results in performance regressions for some users;
> > > apparently the workload on one mount interferes with performance of
> > > another mount, and they were previously able to work around the
> > > problem
> > > by using different server IP addresses for the different mounts.
> > >
> > > Am I overlooking some hack that would reenable the previous behavior?
> > > Or would people be averse to an "-o noshareconn" option?
> >
> > I suppose you could just toggle the nfs4_unique_id parameter.  This
> > seems to
> > work:
> >
> > flock /sys/module/nfs/parameters/nfs4_unique_id bash -c "OLD_ID=\$(cat
> > /sys/module/nfs/parameters/nfs4_unique_id); echo imalittleteapot >
> > /sys/module/nfs/parameters/nfs4_unique_id; mount -ov4,sec=sys
> > 10.0.1.200:/exports /mnt/fedora2; echo \$OLD_ID >
> > /sys/module/nfs/parameters/nfs4_unique_id"
> >
> > I'm trying to think of a reason why this is a bad idea, and not coming
> > up
> > with any.  Can we support users that have already found this solution?
> >
> 
> What about reboot recovery? How will each mount recover its own state
> (and present the same identifier it used before). Client only keeps
> track of one?

Looks like nfs4_init_{non}uniform_client_string() stores it in
cl_owner_id, and I was thinking that meant cl_owner_id would be used
from then on....

But actually, I think it may run that again on recovery, yes, so I bet
changing the nfs4_unique_id parameter midway like this could cause bugs
on recovery.

--b.