Re: [PATCH 0/6 RFC v2] nfsd: allocate/free session-based DRC slots on demand

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2024-11-19 at 11:41 +1100, NeilBrown wrote:
> Here is v2 of my series for on-demand allocation and freeing of session DRC slots.
> 
> - Now uses an xarray to store slots, and the limit is raised to 2048
> - delays retiring a slot until the client has confirmed that it isn't
>   using it as described in RFC:
> 
>       The replier SHOULD retain the slots it wants to retire until the
>       requester sends a request with a highest_slotid less than or equal
>       to the replier's new enforced highest_slotid.
> 
> - When a retired slot is used, allow the seqid to be the next in sequence
>   as required by the RFC:
> 
>          Each time a slot is reused, the request MUST specify a sequence
>          ID that is one greater than that of the previous request on the
>          slot.
>
>   or "1" as (arguably) allowed by the RFC:
> 
>          The first time a slot is used, the requester MUST specify a
>          sequence ID of one
> 

I thought that the conclusion of the IETF discussion was that we should
reset this to 1. It'd be ideal to just do that, as then we wouldn't
need NFSD4_SLOT_REUSED.

Are there any clients that expect to reuse the old seqid in this
situation? I know the Linux client doesn't. Do Solaris or FreeBSD?

> - current slot allocation is now reported in /proc/fs/nfsd/clients/*/info
> 
> This has been tested with highly aggressive shrinker settings:
> 	nfsd_slot_shrinker->seeks = 0;
> 	nfsd_slot_shrinker->batch = 2;
> 
> and with periodic "echo 3 > drop_caches".  The slot count drops as
> expected and then increases again.
> 

This is really great work, Neil!
--
Jeff Layton <jlayton@kernel.org>