linux-kernel - Re: [PATCH v6 1/5] mm/zone_device: Reinitialize large zone device private folios

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Message-ID: <626c34fc-34df-4629-baf3-fbebc9abafbb@nvidia.com>
Date: Thu, 22 Jan 2026 20:10:44 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Vlastimil Babka <vbabka@...e.cz>, Matthew Brost
 <matthew.brost@...el.com>, Zi Yan <ziy@...dia.com>
Cc: Jason Gunthorpe <jgg@...dia.com>, Matthew Wilcox <willy@...radead.org>,
 Alistair Popple <apopple@...dia.com>,
 Francois Dugast <francois.dugast@...el.com>, intel-xe@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, adhavan Srinivasan <maddy@...ux.ibm.com>,
 Nicholas Piggin <npiggin@...il.com>, Michael Ellerman <mpe@...erman.id.au>,
 "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
 Felix Kuehling <Felix.Kuehling@....com>,
 Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
 David Hildenbrand <david@...nel.org>, Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>, Leon Romanovsky
 <leon@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, linuxppc-dev@...ts.ozlabs.org,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
 linux-mm@...ck.org, linux-cxl@...r.kernel.org
Subject: Re: [PATCH v6 1/5] mm/zone_device: Reinitialize large zone device
 private folios

On 1/22/26 19:00, Vlastimil Babka wrote:
> On 1/22/26 08:19, Matthew Brost wrote:
>> On Tue, Jan 20, 2026 at 10:01:18PM -0500, Zi Yan wrote:
>>> On 20 Jan 2026, at 8:53, Jason Gunthorpe wrote:
>>>
>>
>> This whole thread makes my head hurt, as does core MM.
>>
>> IMO the TL;DR is:
>>
>> - Why is Intel the only one proving this stuff works? We can debate all
>>   day about what should or should not work — but someone else needs to
>>   actually prove it.i, rather than type hypotheticals.
>>
>> - Intel has demonstrated that this works and is still getting blocked.
>>
>> - This entire thread is about a fixes patch for large device pages.
>>   Changing prep_compound_page is completely out of scope for a fixes
>>   patch, and honestly so is most of the rest of what’s being proposed.
> 
> FWIW I'm ok if this lands as a fix patch, and perceived the discussion to be
> about how refactor things more properly afterwards, going forward.
> 

I've said the same thing and I concur, we can use the patch as-is and
change this to set the relevant identified fields after 6.19

Balbir

>> - At a minimum, you must clear every page’s flags in the loop. So why not
>>   conservatively clear anything else a folio might have set before calling
>>   an existing core-MM function, ensuring the pages are in a known state?
>>   This is a fixes patch.
>>
>> - Given the current state of the discussion, I don’t think large device
>>   pages should be in 6.19. And if so, why didn’t the entire device pages
>>   series receive this level of scrutiny earlier? It’s my mistake for not
>>   saying “no” until the reallocation at different sizes issue was resolved.
>>
>> @Andrew. - I'd revert large device pages in 6.19 as it doesn't work and
>> we seemly cannot close on this.
>>
>> Matt

<snip>