linux-kernel - Re: [v3 07/11] mm/thp: add split during migration support

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Message-ID: <5cdd07b4-f924-4207-a8cf-09b4fc26d3d7@redhat.com>
Date: Wed, 27 Aug 2025 22:29:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Balbir Singh <balbirs@...dia.com>, dri-devel@...ts.freedesktop.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Zi Yan <ziy@...dia.com>,
 Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
 Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Alistair Popple <apopple@...dia.com>, Oscar Salvador <osalvador@...e.de>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lyude Paul <lyude@...hat.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Ralph Campbell <rcampbell@...dia.com>,
 Mika Penttilä <mpenttil@...hat.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Francois Dugast <francois.dugast@...el.com>
Subject: Re: [v3 07/11] mm/thp: add split during migration support

On 12.08.25 04:40, Balbir Singh wrote:
> Support splitting pages during THP zone device migration as needed.
> The common case that arises is that after setup, during migrate
> the destination might not be able to allocate MIGRATE_PFN_COMPOUND
> pages.
> 
> Add a new routine migrate_vma_split_pages() to support the splitting
> of already isolated pages. The pages being migrated are already unmapped
> and marked for migration during setup (via unmap). folio_split() and
> __split_unmapped_folio() take additional isolated arguments, to avoid
> unmapping and remaping these pages and unlocking/putting the folio.

No detailed review, just a high-level comment: please take better care 
of crafting your patch subjects.

This should probably be

mm/migrate_device: support splitting device folios during migration

-- 
Cheers

David / dhildenb