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

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Message-ID: <4D6D7321-CAEC-4D82-9354-4B9786C4D05E@nvidia.com>
Date: Wed, 18 Jun 2025 14:48:20 -0400
From: Zi Yan <ziy@...dia.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-doc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 virtualization@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Jonathan Corbet <corbet@....net>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
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 Christophe Leroy <christophe.leroy@...roup.eu>,
 Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
 Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
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 Alexander Viro <viro@...iv.linux.org.uk>,
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 Harry Yoo <harry.yoo@...cle.com>, Qi 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()

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.

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.

Best Regards,
Yan, Zi