On Mon, 22 Apr 2024, Chuck Lever 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.
Does each client really need 1MB?
Obviously we don't want all memory to be used by client state....
>
> 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?
The failure mode is repeated client retries that never succeed. I think
an outright failure would be preferable - it would be more clear than
memory must be added.
The server has N active clients and M courtesy clients.
Triggering reclaim when N+M exceeds a limit and M>0 makes sense.
A hard failure (NFS4ERR_RESOURCE) when N exceeds a limit makes sense.
A soft failure (NFS4ERR_DELAY) while reclaim is running makes sense.
I don't think a retry while N exceeds the limit makes sense.
Do we have a count of active vs courtesy clients?
>
> Meanwhile, we need to have broader and more regular testing of NFSD
> on memory-starved systems. That's a long-term project.
:-)
Thanks,
NeilBrown
>
>
> > Signed-off-by: NeilBrown <neilb@xxxxxxx>
> > ---
> > 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
> >
> >
>
> --
> Chuck Lever
>
