Re: [PATCH 0/6] mm: split underutilized THPs

Yu Zhao
2024-08-05T19:51:50Z

On Sun, Aug 4, 2024 at 7:33 PM Rik van Riel <riel@surriel.com> wrote:
>
> On Sun, 2024-08-04 at 15:54 -0600, Yu Zhao wrote:
> > On Thu, Aug 1, 2024 at 9:47 AM David Hildenbrand <david@redhat.com>
> > wrote:
> > >
> > > On 01.08.24 08:09, Yu Zhao wrote:
> > > >
> > > > I would recommend shatter [1] instead of splitting so that
> > > > 1) whoever underutilized their THPs get punished for the
> > > > overhead;
> > > > 2) underutilized THPs are kept intact and can be reused by
> > > > others.
> > > >
> > > > [1]
> > > > https://lore.kernel.org/20240229183436.4110845-3-yuzhao@google.com/
> > > >
> > >
> > > Do you have any plans to upstream the shattering also during
> > > "ordinary"
> > > deferred splitting?
> >
> > Yes, once we finish verifying it in our production.
> >
>
> Shattering does seem like a nice improvement to the THP shrinker!
>
> However, given that the shattering code is still being verified,
> and the THP shrinker policy will no doubt need some tuning once
> more real world workloads get thrown at it, would it make sense
> to do those two things in parallel?
>
> We could move forward with the THP shrinker as-is today, and use
> the increased exposure it gets to fine tune the shrinking policy,
> and then move it over to using the shattering code once that is
> ready.
>
> Is there any good reason to serialize these two things?

I'm fine with whichever way you prefer: if you are eager to try
shattering in your production environment, I'd be incentivized to
throw in extra engineers and get it ready for you asap.