Alistair Popple <apop...@nvidia.com> writes: > 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.
So, folios include file cache, anonymous, and some device private. >> > 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. Yes. The is the current behavior per my understanding too. > Did you have some particular reason/idea for why we might want to do this? No. Just want to check whether there are some requirements for that. I think that it's just another way to organize code. --- Best Regards, Huang, Ying
