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

[Christoph Hellwig]

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:

NFS: Shortcut lookup revalidations if we have a directory delegation