Re: [RFC] simplifying fast_dput(), dentry_kill() et.al.

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

On Tue, Oct 31, 2023 at 06:12:26AM +0000, Al Viro wrote:
> On Tue, Oct 31, 2023 at 01:53:51AM +0000, Al Viro wrote:
> 
> > Carving that series up will be interesting, though...
> 
> I think I have a sane carve-up; will post if it survives testing.

OK, current variant survives local testing.  Lives in
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.dcache

Shortlog:
      fast_dput(): having ->d_delete() is not reason to delay refcount decrement
      fast_dput(): handle underflows gracefully
      fast_dput(): new rules for refcount
      __dput_to_list(): do decrement of refcount in the caller
      retain_dentry(): lift decrement of ->d_count into callers
      __dentry_kill(): get consistent rules for ->d_count
      dentry_kill(): don't bother with retain_dentry() on slow path
      Call retain_dentry() with refcount 0
      fold the call of retain_dentry() into fast_dput()
      don't try to cut corners in shrink_lock_dentry()
      fold dentry_kill() into dput()
      get rid of __dget()
      shrink_dentry_list(): no need to check that dentry refcount is marked dead
      to_shrink_list(): call only if refcount is 0
      switch select_collect{,2}() to use of to_shrink_list()

Diffstat:
 fs/dcache.c | 268 ++++++++++++++++++++++--------------------------------------
 1 file changed, 96 insertions(+), 172 deletions(-)

Individual patches in followups.  Review and testing would be welcome,
and it's obviously next cycle fodder.  Massage of refcounting is in the
first 11 commits, last 4 are followups.