On Wed, Jun 28, 2023 at 10:08:08PM -0700, Hugh Dickins wrote:

On Wed, 28 Jun 2023, Gerald Schaefer wrote:

quoted

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