[PATCH v2 07/12] s390: add pte_free_defer() for pgtables sharing page

[Jason Gunthorpe]

On Wed, Jun 28, 2023 at 10:08:08PM -0700, Hugh Dickins wrote:
> On Wed, 28 Jun 2023, Gerald Schaefer wrote:
> > 
> > As discussed in the other thread, we would rather go with less complexity,
> > possibly switching to an approach w/o the list and fragment re-use in the
> > future. For now, as a first step in that direction, we can try with not
> > adding fragments back only for pte_free_defer(). Here is an adjusted
> > version of your patch, copying most of your pte_free_defer() logic and
> > also description, tested with LTP and all three of your patch series applied:
> 
> Thanks, Gerald: I don't mind abandoning my 13/12 SLAB_TYPESAFE_BY_RCU
> patch (posted with fewer Cc's to the s390 list last week), and switching
> to your simpler who-cares-if-we-sometimes-don't-make-maximal-use-of-page
> patch.
> 
> But I didn't get deep enough into it today to confirm it - and disappointed
> that you've found it necessary to play with pt_frag_refcount in addition to
> _refcount and HH bits.  No real problem with that, but my instinct says it
> should be simpler.

Is there any reason it should be any different at all from what PPC is
doing?

I still think the right thing to do here is make the PPC code common
(with Hugh's proposed RCU modification) and just use it in both
arches....

Jason