On Mon, Mar 15, 2021 at 01:38:04PM +0100, Michal Hocko wrote:

I tend to agree here as well. The level compoud_head has spread out
silently is just too large. There are people coming up with all sorts of
optimizations to workaround that, and they are quite right that this is
somehing worth doing, but last attempts I have seen were very focused on
specific page flags handling which is imho worse wrt maintainability
than a higher level and type safe abstraction. I find it quite nice that
this doesn't really have to be a flag day conversion but it can be done
incrementally.

I didn't get review the series yet and I cannot really promise anything
but from what I understand the conversion should be pretty
straightforward, albeit noisy.

One thing that was really strange to me when seeing the concept for the
first time was the choice of naming (no I do not want to start any
bikeshedding) because it hasn't really resonated with the udnerlying
concept. Maybe just me as a non native speaker... page_head would have
been so much more straightforward but not something I really care about.

That pretty much summarizes my opinion as well.  I'll need to find some
time to review the series as well.