linux-kernel - Re: [RFC v2 0/3] Decoupling large folios dependency on THP

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Message-ID: <aTj2pZqwx5xJVavb@casper.infradead.org>
Date: Wed, 10 Dec 2025 04:27:17 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Zi Yan <ziy@...dia.com>
Cc: Pankaj Raghav <p.raghav@...sung.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>, Michal Hocko <mhocko@...e.com>,
	Lance Yang <lance.yang@...ux.dev>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nico Pache <npache@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, mcgrof@...nel.org,
	gost.dev@...sung.com, kernel@...kajraghav.com, tytso@....edu
Subject: Re: [RFC v2 0/3] Decoupling large folios dependency on THP

On Tue, Dec 09, 2025 at 11:03:23AM -0500, Zi Yan wrote:
> I wonder if core-mm should move mTHP code out of CONFIG_TRANSPARENT_HUGEPAGE
> and mTHP might just work. Hmm, folio split might need to be moved out of
> mm/huge_memory.c in that case. khugepaged should work for mTHP without
> CONFIG_TRANSPARENT_HUGEPAGE as well. OK, for anon folios, the changes might
> be more involved.

I think this is the key question to be discussed at LPC.  How much of
the current THP code should we say "OK, this is large folio support
and everybody needs it" and how much is "This is PMD (or mTHP) support;
this architecture doesn't have it, we don't need to compile it in".