Re: [External] : Re: NFS dentry caching regression? was Re: [GIT PULL] Please pull NFS client updates for Linux 6.19

[Anna Schumaker <anna.schumaker@oracle.com>]

Hi Christoph,

On 12/17/25 4:53 AM, Christoph Hellwig wrote:
> On Wed, Dec 17, 2025 at 01:32:30AM -0800, Christoph Hellwig wrote:
>> Hi all,
>>
>> the merge of this branch causes NFS lookup operation to shoot up a lot
>> for me.  And with merge I mean merge - both parent of the merge on their
>> own are fine.
>>
>> With the script below that simulates running python scripts with lots
>> of imports that was created to benchmark delegation performance, the
>> number of lookups in the measurement period shoots up from 4 to about
>> 410000, which is a bit suboptimal.  I have no idea how this could
>> happen, but it must be related to some sort of pathname lookup changes
>> I guess.  Other operations looks roughly the same.
> 
> To further pin this down, I rebased the patches from the NFS pull request
> on top of the baseline (d358e5254674b70f34c847715ca509e46eb81e6f) and
> bisected that.  This ends up in:

Thanks for reporting this, and for the reproducer script. I'll dig into this
today and try to fix what I broke!

Anna

> 
> NFS: Shortcut lookup revalidations if we have a directory delegation
>