Re: add a LRU for delegations

[Christoph Hellwig <hch@lst.de>]

On Wed, Jan 07, 2026 at 09:22:49PM +0200, Sagi Grimberg wrote:
> I think that there is merit for tracking file usage frequency and 
> accounting it for deleg return
> policy, and I don't necessarily think that it would not be worth the 
> overhead (compared to sending rpcs to the server)...
> but I agree that its a much heavier lift (it can always be done 
> incrementally to this patchset).

There's a reason the rest of the kernel uses fairly simple LRU (or
rather modified LRU / clock like) eviction policies like this, in
that the sampling is quite overboard.   I'm not going to keep you
from looking into this, but I don't think it's worthwhile.

> And, in genenral, I think that the server is in a much better position to 
> solicit preemptive delegation recalls as opposed
> to the client voluntarily return delegations when crossing a somewhat 
> arbitrary delegation_watermark.

Yes.  For that we'd need working RECALL_ANY support, though.  And
the way that works in the spec where the value is a number to keep
instead of a number to returns makes it pretty weird unfortunately.