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

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Message-ID: <a3e367bbb2d3f32532b54ad91facec3ff4fee686.camel@surriel.com>
Date: Sun, 04 Aug 2024 21:32:57 -0400
From: Rik van Riel <riel@...riel.com>
To: Yu Zhao <yuzhao@...gle.com>, David Hildenbrand <david@...hat.com>
Cc: 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, 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?

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