Re: NFSv4 client locks up on larger writes with Kerberos enabled

[Kevin Vasko <kvasko@gmail.com>]

What does the GSS window control? I mentioned it in another thread somewhere but I found out that clients with a slower connection seem to not exhibit this issue.

All of these clients are local to the NFS server (in same room, which is in Korea). I’ve got clients in the USA and they don’t seem to exhibit this lockup behavior. I haven’t done extensive testing but we can get 3-4MB/s across the ocean and as of yet I haven’t see a client from the USA lock up like the ones local. It obviously takes a lot longer but haven’t seen it lock up on transferring several 5GB+ files. 

Could the GSS window not be overflowing with the slower connection and we wouldn’t see the issue? 

-Kevin

> On Sep 26, 2019, at 2:55 PM, Bruce Fields <bfields@fieldses.org> wrote:
> 
> On Thu, Sep 26, 2019 at 08:55:17AM -0700, Chuck Lever wrote:
>>>> On Sep 25, 2019, at 1:07 PM, Bruce Fields <bfields@fieldses.org> wrote:
>>> In that case--I seem to remember there's a way to configure the size of
>>> the client's slot table, maybe lowering that (decreasing the number of
>>> rpc's allowed to be outstanding at a time) would work around the
>>> problem.
>> 
>>> Should the client be doing something different to avoid or recover from
>>> overflows of the gss window?
>> 
>> The client attempts to meter the request stream so that it stays
>> within the bounds of the GSS sequence number window. The stream
>> of requests is typically unordered coming out of the transmit
>> queue.
>> 
>> There is some new code (since maybe v5.0?) that handles the
>> metering: gss_xmit_need_reencode().
> 
> I guess I was thinking he could write a small number (say 2 digits) into
> /sys/module/sunrpc/parameters/tcp_max_slot_table_entries (before
> mounting, I guess?) and see if the problem's reproducable.
> 
> If not, that's a little more evidence that it's the gss sequence window.
> 
> (And might be an adequate workaround for now.)
> 
> --b.