Jason Gunthorpe <jgg@xxxxxxxxxx> writes: > 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.. Yep, no worries. > Thanks, > Jason
