Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210609215319.5518-1-olga.kornievskaia@gmail.com>
 <20210609215319.5518-3-olga.kornievskaia@gmail.com> <6C64456A-931F-4CAD-A559-412A12F0F741@oracle.com>
 <6bca80de292b5aa36734e7d942d0e9f53430903b.camel@hammerspace.com>
 <83D9342E-FDAF-4B2C-A518-20BF0A9AD073@oracle.com> <3658c226b43fb190de38c00e5199ccf35ccc4369.camel@hammerspace.com>
In-Reply-To: <3658c226b43fb190de38c00e5199ccf35ccc4369.camel@hammerspace.com>
From:   Olga Kornievskaia <olga.kornievskaia@gmail.com>
Date:   Thu, 10 Jun 2021 10:31:38 -0400
Message-ID: <CAN-5tyF3BSDvsegLWM6hAOY9QDMbG1LUg9YykXi8rwDcNVXqbA@mail.gmail.com>
Subject: Re: [PATCH v2 2/3] NFSv4 introduce max_connect mount options
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "chuck.lever@oracle.com" <chuck.lever@oracle.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "anna.schumaker@netapp.com" <anna.schumaker@netapp.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jun 10, 2021 at 10:13 AM Trond Myklebust
<trondmy@hammerspace.com> wrote:
>
> On Thu, 2021-06-10 at 13:56 +0000, Chuck Lever III wrote:
> >
> >
> > > On Jun 10, 2021, at 9:34 AM, Trond Myklebust <
> > > trondmy@hammerspace.com> wrote:
> > >
> > > On Thu, 2021-06-10 at 13:30 +0000, Chuck Lever III wrote:
> > > >
> > > >
> > > > > On Jun 9, 2021, at 5:53 PM, Olga Kornievskaia <
> > > > > olga.kornievskaia@gmail.com> wrote:
> > > > >
> > > > > From: Olga Kornievskaia <kolga@netapp.com>
> > > > >
> > > > > This option will control up to how many xprts can the client
> > > > > establish to the server. This patch parses the value and sets
> > > > > up structures that keep track of max_connect.
> > > > >
> > > > > Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> > > > > ---
> > > > > fs/nfs/client.c           |  1 +
> > > > > fs/nfs/fs_context.c       |  8 ++++++++
> > > > > fs/nfs/internal.h         |  2 ++
> > > > > fs/nfs/nfs4client.c       | 12 ++++++++++--
> > > > > fs/nfs/super.c            |  2 ++
> > > > > include/linux/nfs_fs_sb.h |  1 +
> > > > > 6 files changed, 24 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/fs/nfs/client.c b/fs/nfs/client.c
> > > > > index 330f65727c45..486dec59972b 100644
> > > > > --- a/fs/nfs/client.c
> > > > > +++ b/fs/nfs/client.c
> > > > > @@ -179,6 +179,7 @@ struct nfs_client *nfs_alloc_client(const
> > > > > struct nfs_client_initdata *cl_init)
> > > > >
> > > > >         clp->cl_proto = cl_init->proto;
> > > > >         clp->cl_nconnect = cl_init->nconnect;
> > > > > +       clp->cl_max_connect = cl_init->max_connect ? cl_init-
> > > > > > max_connect : 1;
> > > >
> > > > So, 1 is the default setting, meaning the "add another transport"
> > > > facility is disabled by default. Would it be less surprising for
> > > > an admin to allow some extra connections by default?
> > > >
> > > >
> > > > >         clp->cl_net = get_net(cl_init->net);
> > > > >
> > > > >         clp->cl_principal = "*";
> > > > > diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
> > > > > index d95c9a39bc70..cfbff7098f8e 100644
> > > > > --- a/fs/nfs/fs_context.c
> > > > > +++ b/fs/nfs/fs_context.c
> > > > > @@ -29,6 +29,7 @@
> > > > > #endif
> > > > >
> > > > > #define NFS_MAX_CONNECTIONS 16
> > > > > +#define NFS_MAX_TRANSPORTS 128
> > > >
> > > > This maximum seems excessive... again, there are diminishing
> > > > returns to adding more connections to the same server. what's
> > > > wrong with re-using NFS_MAX_CONNECTIONS for the maximum?
> > > >
> > > > As always, I'm a little queasy about adding yet another mount
> > > > option. Are there real use cases where a whole-client setting
> > > > (like a sysfs attribute) would be inadequate? Is there a way
> > > > the client could figure out a reasonable maximum without a
> > > > human intervention, say, by counting the number of NICs on
> > > > the system?
> > >
> > > Oh, hell no! We're not tying anything to the number of NICs...
> >
> > That's a bit of an over-reaction. :-) A little more explanation
> > would be welcome. I mean, don't you expect someone to ask "How
> > do I pick a good value?" and someone might reasonably answer
> > "Well, start with the number of NICs on your client times 3" or
> > something like that.
> >
> > IMO we're about to add another admin setting without understanding
> > how it will be used, how to select a good maximum value, or even
> > whether this maximum needs to be adjustable. In a previous e-mail
> > Olga has already demonstrated that it will be difficult to explain
> > how to use this setting with nconnect=.
> >
> > Thus I would favor a (moderate) soldered-in maximum to start with,
> > and then as real world use cases arise, consider adding a tuning
> > mechanism based on actual requirements.
>
> It's not an overreaction. It's insane to think that counting NICs gives
> you any notion whatsoever about the network topology and connectivity
> between the client and server. It doesn't even tell you how many of
> those NICs might potentially be available to your application.
>
> We're not doing any automation based on that kind of layering
> violation.

I'm not suggesting to programmatically determine the number of NIC to
determine the value of max_connect.

>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>