Re: [Patch 0/2] NFSD: Fix server hang when there are multiple layout conflicts

[Dai Ngo]

On 11/11/25 7:34 AM, Chuck Lever wrote:
> On 11/11/25 10:24 AM, Dai Ngo wrote:
> > > Last thought (for now): I think Neil has some work for dynamic knfsd
> > > thread
> > > count.. or Jeff?  (I am having trouble finding it) Would that work around
> > > this problem?
> > This would help, and I prefer this route rather than rework __break_lease
> > to return EAGAIN/jukebox while the server recalling the layout.
> Jeff is looking at continuing Neil's work in this area.
>
> Adding more threads, IMHO, is not a good long term solution for this
> particular issue. There's no guarantee that the server won't get stuck
> no matter how many threads are created, and practically speaking, there
> are only so many threads that can be created before the server goes
> belly up. Or put another way, there's no way to formally prove that the
> server will always be able to make forward progress with this solution.
>
> We want NFSD to have a generic mechanism for deferring work so that an
> nfsd thread never waits more than a few dozen milliseconds for anything.
> This is the tactic NFSD uses for delegation recalls, for example.

I think we need both: (1) dynamic number of server threads and (2) the
ability to defer work as we currently do for the delegation recall. I'd
think we need (1) first as it applies for general server operations and
not just layout recalls.

Even if we had both of these enhancements, we still need to enforce timeout
for __break_lease since we don't want to wait for the recall forever.

-Dai


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