On Fri, Jun 24, 2022 at 10:11:01AM +1000, Alistair Popple wrote: > > Hum.. Alistair, maybe you should look at this as well, I'm struggling > > alot to understand how it is safe to drop the reference on the page > > but hold a pointer to it on the movable_page_list - sure it was > > isolated - but why does that mean it won't be concurrently unmapped > > and freed? > > folio_isolate_lru() takes a reference on the page so you're safe from it > being freed. If it gets unmapped it will be freed when the matching > putback_movable_pages() is called. Hm, I guess I didn't dig deep enough into that call chain.. > > Anyhow, it looks like the problem is the tortured logic in this > > function, what do you think about this: > > At a glance it seems reasonable, although I fear it might conflict with > my changes for device coherent migration. Agree the whole > check_and_migrate_movable_pages() logic is pretty tortured though, and I > don't think I'm making it better so would be happy to try cleaning it up > futher once the device coherent changes are in. OK, can I leave this patch with you then? I have no way to test it.. Thanks, Jason
