linux-kernel - Re: [PATCH v2 03/17] mm/rmap: convert make_device_exclusive_range() to make_device

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Message-ID: <76a9a0dc-4d2f-430c-a2be-a2371f3108d7@redhat.com>
Date: Mon, 17 Feb 2025 10:32:38 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-mm@...ck.org, nouveau@...ts.freedesktop.org,
 linux-trace-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 damon@...ts.linux.dev, Jérôme Glisse
 <jglisse@...hat.com>, Jonathan Corbet <corbet@....net>,
 Alex Shi <alexs@...nel.org>, Yanteng Si <si.yanteng@...ux.dev>,
 Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Masami Hiramatsu <mhiramat@...nel.org>,
 Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 SeongJae Park <sj@...nel.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pasha Tatashin <pasha.tatashin@...een.com>, Peter Xu <peterx@...hat.com>,
 Jason Gunthorpe <jgg@...dia.com>, Simona Vetter <simona.vetter@...ll.ch>
Subject: Re: [PATCH v2 03/17] mm/rmap: convert make_device_exclusive_range()
 to make_device_exclusive()

On 17.02.25 01:01, Alistair Popple wrote:
> On Tue, Feb 11, 2025 at 09:33:54AM +0100, David Hildenbrand wrote:
>> On 11.02.25 06:00, Andrew Morton wrote:
>>> On Mon, 10 Feb 2025 20:37:45 +0100 David Hildenbrand <david@...hat.com> wrote:
>>>
>>>> The single "real" user in the tree of make_device_exclusive_range() always
>>>> requests making only a single address exclusive. The current implementation
>>>> is hard to fix for properly supporting anonymous THP / large folios and
>>>> for avoiding messing with rmap walks in weird ways.
>>>>
>>>> So let's always process a single address/page and return folio + page to
>>>> minimize page -> folio lookups. This is a preparation for further
>>>> changes.
>>>>
>>>> Reject any non-anonymous or hugetlb folios early, directly after GUP.
>>>>
>>>> While at it, extend the documentation of make_device_exclusive() to
>>>> clarify some things.
>>>
>>> x86_64 allmodconfig:
>>>
>>> drivers/gpu/drm/nouveau/nouveau_svm.c: In function 'nouveau_atomic_range_fault':
>>> drivers/gpu/drm/nouveau/nouveau_svm.c:612:68: error: 'folio' undeclared (first use in this function)
>>>     612 |                 page = make_device_exclusive(mm, start, drm->dev, &folio);
>>>         |                                                                    ^~~~~
>>> drivers/gpu/drm/nouveau/nouveau_svm.c:612:68: note: each undeclared identifier is reported only once for each function it appears in
>>
>> Ah! Because I was carrying on the same branch SVM fixes [1] that are
>> getting surprisingly little attention so far.
> 
> I believe this has been picked up in drm-misc-fixes now:
> 
> https://lore.kernel.org/dri-devel/Z69eloo_7LM6NneO@cassiopeiae/

Yes. Both trees should merge without conflicts. However, we can later 
get rid of the now-superfluous page_folio() that was required in the drm 
fix.

-- 
Cheers,

David / dhildenb