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

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Message-ID: <aFMH0TmoPylhkSjZ@casper.infradead.org>
Date: Wed, 18 Jun 2025 19:39:13 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Zi Yan <ziy@...dia.com>
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,
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	Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to
 isolate_movable_ops_page()

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.