linux-kernel - Re: [PATCH] mm/huge_memory.c: introduce folio_split

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Message-ID: <210B3EB5-F24C-4A4A-896F-1C9B30A7C6F5@nvidia.com>
Date: Thu, 13 Nov 2025 21:11:20 -0500
From: Zi Yan <ziy@...dia.com>
To: Balbir Singh <balbirs@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 dri-devel@...ts.freedesktop.org, Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.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: [PATCH] mm/huge_memory.c: introduce folio_split_unmapped

On 13 Nov 2025, at 20:22, Balbir Singh wrote:

> Unmapped was added as a parameter to __folio_split() and related
> call sites to support splitting of folios already in the midst
> of a migration. This special case arose for device private folio
> migration since during migration there could be a disconnect between
> source and destination on the folio size.
>
> Introduce folio_split_unmapped() to handle this special case. Also
> refactor code and add __folio_freeze_and_split_unmapped() helper that
> is common to both __folio_split() and folio_split_unmapped().
>
> This in turn removes the special casing introduced by the unmapped
> parameter in __folio_split().
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Joshua Hahn <joshua.hahnjy@...il.com>
> Cc: Rakie Kim <rakie.kim@...com>
> Cc: Byungchul Park <byungchul@...com>
> Cc: Gregory Price <gourry@...rry.net>
> Cc: Ying Huang <ying.huang@...ux.alibaba.com>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> Cc: Nico Pache <npache@...hat.com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Dev Jain <dev.jain@....com>
> Cc: Barry Song <baohua@...nel.org>
> Cc: Lyude Paul <lyude@...hat.com>
> Cc: Danilo Krummrich <dakr@...nel.org>
> Cc: David Airlie <airlied@...il.com>
> Cc: Simona Vetter <simona@...ll.ch>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: Mika Penttilä <mpenttil@...hat.com>
> Cc: Matthew Brost <matthew.brost@...el.com>
> Cc: Francois Dugast <francois.dugast@...el.com>
>
> Suggested-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: Balbir Singh <balbirs@...dia.com>
> ---
>  include/linux/huge_mm.h |   5 +-
>  mm/huge_memory.c        | 332 ++++++++++++++++++++++------------------
>  mm/migrate_device.c     |   3 +-
>  3 files changed, 191 insertions(+), 149 deletions(-)
>
LGTM. Acked-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi