linux-kernel - Re: [PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to isolate_movable_ops

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Message-ID: <87h5zyrdl9.fsf@DESKTOP-5N7EMDA>
Date: Sun, 29 Jun 2025 19:28:50 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>
Cc: Matthew Wilcox <willy@...radead.org>,  linux-kernel@...r.kernel.org,
  linux-mm@...ck.org,  linux-doc@...r.kernel.org,
  linuxppc-dev@...ts.ozlabs.org,  virtualization@...ts.linux.dev,
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 Zheng <zhengqi.arch@...edance.com>,  Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to
 isolate_movable_ops_page()

David Hildenbrand <david@...hat.com> writes:

> 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.

Is it possible to use some device specific callbacks (DMA?) to copy
from/to the device private folios (or pages) to/from the normal
file/anon folios in the future?

---
Best Regards,
Huang, Ying