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Date: Tue, 23 Apr 2024 17:12:56 +0200
From: Petr Vorel <pvorel@suse.cz>
To: Chuck Lever <chuck.lever@oracle.com>
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.
Message-ID: <20240423151256.GA203608@pevik>
Reply-To: Petr Vorel <pvorel@suse.cz>
References: <171375175915.7600.6526208866216039031@noble.neil.brown.name>
 <ZiZnbV+htcvGuGQl@tissot.1015granger.net>
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In-Reply-To: <ZiZnbV+htcvGuGQl@tissot.1015granger.net>

> 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.

Kind regards,
Petr

> However, that commit claims that the client is told to retry; I
> don't expect client creation to fail outright. Can you describe the
> failure mode you see?

> Meanwhile, we need to have broader and more regular testing of NFSD
> on memory-starved systems. That's a long-term project.


> > Signed-off-by: NeilBrown <neilb@suse.de>
> > ---
> >  fs/nfsd/nfs4state.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)

> > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> > index daf83823ba48..8a40bb6a4a67 100644
> > --- a/fs/nfsd/nfs4state.c
> > +++ b/fs/nfsd/nfs4state.c
> > @@ -2223,10 +2223,9 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name,
> >  	struct nfs4_client *clp;
> >  	int i;

> > -	if (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients) {
> > +	if (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients)
> >  		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> > -		return NULL;
> > -	}
> > +
> >  	clp = kmem_cache_zalloc(client_slab, GFP_KERNEL);
> >  	if (clp == NULL)
> >  		return NULL;
> > -- 
> > 2.44.0