On Sun, Jun 29, 2025 at 07:28:50PM +0800, Huang, Ying wrote: > David Hildenbrand <da...@redhat.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)
Yes, they should be proper 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? I guess we could put such callbacks on the folio->pgmap, but I'm not sure why we would want to. Currently all migration to/from device private (or coherent) folios is managed by the device, which is one of the features of ZONE_DEVICE. Did you have some particular reason/idea for why we might want to do this? > --- > Best Regards, > Huang, Ying
