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

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Message-ID: <8FE2EDF1-DF20-4DC4-A179-83E598508748@nvidia.com>
Date: Mon, 23 Jun 2025 11:42:06 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.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, linux-fsdevel@...r.kernel.org,
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 Madhavan Srinivasan <maddy@...ux.ibm.com>,
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 Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
 Arnd Bergmann <arnd@...db.de>,
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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 23 Jun 2025, at 11:33, David Hildenbrand wrote:

> 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.

Got it. (I was abusing it to help develop alloc_contig_range() at pageblock
granularity, since it was easy to write a driver to allocate a compound page
at a specific PFN and claim the page is movable, then do page online/offline
the range containing the PFNs. :) )

For the patch, Reviewed-by: Zi Yan <ziy@...dia.com>

--
Best Regards,
Yan, Zi