Message-ID: <bef13481-5218-4732-831d-fe22d95184c1@redhat.com>
Date: Mon, 23 Jun 2025 17:33:15 +0200
From: David Hildenbrand <david@...hat.com>
To: Zi Yan <ziy@...dia.com>, Matthew Wilcox <willy@...radead.org>
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Subject: Re: [PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to
 isolate_movable_ops_page()

On 18.06.25 20:48, Zi Yan wrote:
> On 18 Jun 2025, at 14:39, Matthew Wilcox wrote:
> 
>> On Wed, Jun 18, 2025 at 02:14:15PM -0400, Zi Yan wrote:
>>> On 18 Jun 2025, at 13:39, David Hildenbrand wrote:
>>>
>>>> ... and start moving back to per-page things that will absolutely not be
>>>> folio things in the future. Add documentation and a comment that the
>>>> remaining folio stuff (lock, refcount) will have to be reworked as well.
>>>>
>>>> While at it, convert the VM_BUG_ON() into a WARN_ON_ONCE() and handle
>>>> it gracefully (relevant with further changes), and convert a
>>>> WARN_ON_ONCE() into a VM_WARN_ON_ONCE_PAGE().
>>>
>>> The reason is that there is no upstream code, which use movable_ops for
>>> folios? Is there any fundamental reason preventing movable_ops from
>>> being used on folios?
>>
>> folios either belong to a filesystem or they are anonymous memory, and
>> so either the filesystem knows how to migrate them (through its a_ops)
>> or the migration code knows how to handle anon folios directly.

Right, migration of folios will be handled by migration core.

> 
> for device private pages, to support migrating >0 order anon or fs folios
> to device, how should we represent them for devices? if you think folio is
> only for anon and fs.

I assume they are proper folios, so yes. Just like they are handled 
today (-> folios)

I was asking a related question at LSF/MM in Alistair's session: are we 
sure these things will be folios even before they are assigned to a 
filesystem? I recall the answer was "yes".

So we don't (and will not) support movable_ops for folios.

-- 
Cheers,

David / dhildenb

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