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Date: Tue, 23 Apr 2024 11:26:05 -0400
From: Chuck Lever <chuck.lever@oracle.com>
To: Petr Vorel <pvorel@suse.cz>
Cc: NeilBrown <neilb@suse.de>, Jeff Layton <jlayton@kernel.org>,
        Olga Kornievskaia <kolga@netapp.com>, Dai Ngo <Dai.Ngo@oracle.com>,
        Tom Talpey <tom@talpey.com>, linux-nfs@vger.kernel.org
Subject: Re: [PATCH] nfsd: don't fail OP_SETCLIENTID when there are lots of
 clients.
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On Tue, Apr 23, 2024 at 05:12:56PM +0200, Petr Vorel wrote:
> > On Mon, Apr 22, 2024 at 12:09:19PM +1000, NeilBrown wrote:
> > > The calculation of how many clients the nfs server can manage is only an
> > > heuristic.  Triggering the laundromat to clean up old clients when we
> > > have more than the heuristic limit is valid, but refusing to create new
> > > clients is not.  Client creation should only fail if there really isn't
> > > enough memory available.
> 
> > > This is not known to have caused a problem is production use, but
> > > testing of lots of clients reports an error and it is not clear that
> > > this error is justified.
> 
> > It is justified, see 4271c2c08875 ("NFSD: limit the number of v4
> > clients to 1024 per 1GB of system memory"). In cases like these,
> > the recourse is to add more memory to the test system.
> 
> FYI the system is using 1468 MB + 2048 MB swap
> 
> $ free -m
>                total        used        free      shared  buff/cache   available
> Mem:            1468         347         589           4         686        1121
> Swap:           2048           0        2048
> 
> Indeed increasing the memory to 3430 MB makes test happy. It's of course up to
> you to see whether this is just unrealistic / artificial problem which does not
> influence users and thus is v2 Neil sent is not worth of merging.

IMO, if you want to handle a large client cohort, NFSD will need to
have adequate memory available. In production scenarios, I think it
is not realistic to expect a 1.5GB server to handle more than a few
dozen NFSv4 clients, given the amount of lease, session, and
open/lock state that can be in flight.

However, in testing scenarios, it's reasonable and even necessary to
experiment with low-memory servers.

I don't disagree that failing the mount attempt outright is a good
thing to do. But to make that fly, we need to figure out how to make
NFSv4.1+ behave that way too.

-- 
Chuck Lever