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

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Message-ID: <CAOUHufZG1qQuA=cvG+46VwvTrn8yU8nY06vC0JLuUj2hthcSWQ@mail.gmail.com>
Date: Mon, 5 Aug 2024 13:51:11 -0600
From: Yu Zhao <yuzhao@...gle.com>
To: Rik van Riel <riel@...riel.com>
Cc: David Hildenbrand <david@...hat.com>, Usama Arif <usamaarif642@...il.com>, akpm@...ux-foundation.org, 
	linux-mm@...ck.org, hannes@...xchg.org, shakeel.butt@...ux.dev, 
	roman.gushchin@...ux.dev, baohua@...nel.org, ryan.roberts@....com, 
	rppt@...nel.org, willy@...radead.org, cerasuolodomenico@...il.com, 
	corbet@....net, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
	kernel-team@...a.com
Subject: Re: [PATCH 0/6] mm: split underutilized THPs

On Sun, Aug 4, 2024 at 7:33 PM Rik van Riel <riel@...riel.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@...hat.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.