Re: NFS delegations behavior analysis

On 23 Jun 2026, at 9:40, Jeff Layton wrote:

> On Tue, 2026-06-23 at 09:32 -0400, Benjamin Coddington wrote:
>> On 23 Jun 2026, at 9:11, Benjamin Coddington wrote:
>>
>>> .... er - so with directory delegations, can we simply re-hydrate the dentry
>>> cache from the directory page mappings if the delegation is still valid?
>>> Does the directory delegation pin the mapping?  Clearly I need to look at
>>> the code..
>>
>> .. right - we don't keep the file attributes in the mappings today.  And,
>> more to the point - the directory delegation doesn't protect those file
>> attributes either.  We'd need NOTIFY4_CHANGE_CHILD_ATTRIBUTES implemented.
>>
>
> Which I think could be done, at least on the Linux server. fsnotify
> does support watching for child attribute changes (FS_EVENT_ON_CHILD |
> FS_ATTRIB).
>
> That could be very chatty though. We would need to do the work to make
> nfsd send callbacks >1 page in order to keep up, I imagine.

I agree - it could easily end up having the opposite effect of optimizing
performance by amplifying op counts for information the client might not
actually use.

Ben