linux-kernel - Re: [PATCH v12 mm-new 15/15] Documentation: mm: update the admin guide for mTHP collapse

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Message-ID: <ed0887eb-6124-44ab-9d1f-1e87e9640e14@redhat.com>
Date: Wed, 22 Oct 2025 22:22:08 +0200
From: David Hildenbrand <david@...hat.com>
To: "Christoph Lameter (Ampere)" <cl@...two.org>,
 Nico Pache <npache@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
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 pfalcato@...e.de, Bagas Sanjaya <bagasdotme@...il.com>
Subject: Re: [PATCH v12 mm-new 15/15] Documentation: mm: update the admin
 guide for mTHP collapse

On 22.10.25 21:52, Christoph Lameter (Ampere) wrote:
> On Wed, 22 Oct 2025, Nico Pache wrote:
> 
>> Currently, madvise_collapse only supports collapsing to PMD-sized THPs +
>> and does not attempt mTHP collapses. +
> 
> madvise collapse is frequently used as far as I can tell from the THP
> loads being tested. Could we support madvise collapse for mTHP?

The big question is still how user space can communicate the desired 
order, and how we can not break existing users.

So I guess there will definitely be some support to trigger collapse to 
mTHP in the future, the big question is through which interface. So it 
will happen after this series.

Maybe through process_madvise() where we have an additional parameter, I 
think that was what people discussed in the past.

-- 
Cheers

David / dhildenb