Re: [PATCH v4 2/7] mm: multi-gen LRU: Have secondary MMUs participate in aging

[Yu Zhao <yuzhao@google.com>]

On Fri, May 31, 2024 at 1:03 AM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> On Fri, May 31, 2024 at 12:05:48AM -0600, Yu Zhao wrote:

Let me add back what I said earlier:

  I'm not convinced, but it doesn't mean your point of view is
  invalid. If you fully understand the implications of your design
  choice and document them, I will not object.

> > All optimizations in v2 were measured step by step. Even that bitmap,
> > which might be considered overengineered, brought a readily
> > measuarable 4% improvement in memcached throughput on Altra Max
> > swapping to Optane:
>
> That's great, but taking an iterative approach to the problem allows
> the reviewers and maintainers to come to their own conclusions about
> each optimization independently. Squashing all of that together and
> posting the result doesn't allow for this.

That's your methodology, which I respect: as I said I won't stand in your way.

But mine is backed by data, please do respect that as well, by doing
what I asked: document your justifications.

> Even if we were to take the series as-is, the door is wide open to
> subsequent improvements.
>
> > What I don't think is acceptable is simplifying those optimizations
> > out without documenting your justifications (I would even call it a
> > design change, rather than simplification, from v3 to v4).
>
> No, sorry, there's nothing wrong with James' approach here.

Sorry, are you saying "without documenting your justifications" is
nothing wrong? If so, please elaborate.

> The discussion that led to the design of v4 happened on list; you were
> on CC. The general consensus on the KVM side was that the bitmap was
> complicated and lacked independent justification. There was ample
> opportunity to voice your concerns before he spent the time on v4.

Please re-read my previous emails -- I never object to the removal of
the bitmap or James' approach.

And please stop making assumptions -- I did voice my concerns with
James privately.

> You seriously cannot fault a contributor for respinning their work based
> on the provided feedback.

Are you saying I faulted James for taking others' feedback? If so,
where? And I'll make sure I don't give such an impression in the
future.

Also what do you think about the technical flaws and inaccurate
understandings I pointed out? You seem to have a strong opinion on
your iterate approach, but I hope you didn't choose to overlook the
real meat of this discussion.