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From:   Olga Kornievskaia <aglo@umich.edu>
Date:   Tue, 6 Oct 2020 17:46:11 -0400
Message-ID: <CAN-5tyGDC0VQqjqUNzs_Ka+-G_1eCScVxuXvWsp7xe7QYj69Ww@mail.gmail.com>
Subject: Re: unsharing tcp connections from different NFS mounts
To:     Benjamin Coddington <bcodding@redhat.com>
Cc:     "J. Bruce Fields" <bfields@fieldses.org>,
        linux-nfs <linux-nfs@vger.kernel.org>
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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?

> Ben
>