linux-kernel - Re: [v5 01/15] mm/zone_device: support large zone device private folios

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Message-ID: <3674bdb2-0e59-4f0d-8adf-4794a6db546c@redhat.com>
Date: Fri, 12 Sep 2025 11:20:03 +0200
From: David Hildenbrand <david@...hat.com>
To: Balbir Singh <balbirs@...dia.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Cc: damon@...ts.linux.dev, dri-devel@...ts.freedesktop.org,
 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: [v5 01/15] mm/zone_device: support large zone device private
 folios

On 12.09.25 06:49, Balbir Singh wrote:
> On 9/11/25 22:52, David Hildenbrand wrote:
>> On 11.09.25 14:49, Balbir Singh wrote:
>>> On 9/11/25 21:45, David Hildenbrand wrote:
>>>> On 08.09.25 02:04, Balbir Singh wrote:
>>>>> Add routines to support allocation of large order zone device folios
>>>>> and helper functions for zone device folios, to check if a folio is
>>>>> device private and helpers for setting zone device data.
>>>>>
>>>>> When large folios are used, the existing page_free() callback in
>>>>> pgmap is called when the folio is freed, this is true for both
>>>>> PAGE_SIZE and higher order pages.
>>>>>
>>>>> Zone device private large folios do not support deferred split and
>>>>> scan like normal THP folios.
>>>>>
>>>>> 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>
>>>>>
>>>>> Signed-off-by: Balbir Singh <balbirs@...dia.com>
>>>>> ---
>>>>
>>>> You missed my comments of this patch in v3.
>>>>
>>>
>>> Hi, David
>>>
>>> Looks I missed your comments, just checked those were largely about alignment and
>>> integrating the code for DEVICE_COHERENT and DEVICE_PRIVATE cases into similar looking
>>> bits for zone device folio free and code-alignment. I'll take a look and update as needed.
>>
>> Yes, and the confusing folio->mapping = NULL that I cannot connect to THP support.
>>
> 
> I can remove that, let me reunify those bits, seems relatively straight forward

BTW, I was wondering when we invalidate folio_test_anon() by clearing 
folio->mapping int he current code flow?

I mean, this must happen at some point when freeing device folios.

-- 
Cheers

David / dhildenb