Re: [PATCH] vfs: move dentry shrinking outside the inode lock in 'rmdir()'

[Al Viro <viro@zeniv.linux.org.uk>]

On Sat, May 11, 2024 at 11:26:26AM -0700, Linus Torvalds wrote:
> Yafang Shao reports that he has seen loads that generate billions of
> negative dentries in a directory, which then when the directory is
> removed causes excessive latencies for other users because the dentry
> shrinking is done under the directory inode lock.
> 
> There seems to be no actual reason for holding the inode lock any more
> by the time we get rid of the now uninteresting negative dentries, and
> it's an effect of just code layout (the shared error path).
> 
> Reorganize the code trivially to just have a separate success path,
> which simplifies the code (since 'd_delete_notify()' is only called in
> the success path anyway) and makes it trivial to just move the dentry
> shrinking outside the inode lock.

Wait, I thought he had confirmed that in the setup in question directories
were *not* removed, hadn't he?

I've no objections against that patch, but if the above is accurate it's
not going to help...