Re: [PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to isolate_movable_ops_page()

[David Hildenbrand]

On 23.06.25 17:42, Zi Yan wrote:
> 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. :) )

Oh, interesting :)

Yeah, with a folio that will be a bit harder ...

> For the patch, Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

Thanks!

--
Cheers,

David / dhildenb