> > memfd_restricted() itself is implemented as a shim layer on top of real > memory file systems (currently tmpfs). Pages in restrictedmem are marked > as unmovable and unevictable, this is required for current confidential > usage. But in future this might be changed. > > I didn't dig full histroy, but I interpret this as we don't support page migration and swapping for restricted memfd for now. IMHO "page marked as unmovable" can be confused with PageMovable(), which is a different thing from this series. It's better to just say something like "those pages cannot be migrated and swapped". [...] > + > + /* > + * These pages are currently unmovable so don't place them into movable > + * pageblocks (e.g. CMA and ZONE_MOVABLE). > + */ > + mapping = memfd->f_mapping; > + mapping_set_unevictable(mapping); > + mapping_set_gfp_mask(mapping, > + mapping_gfp_mask(mapping) & ~__GFP_MOVABLE); But, IIUC removing __GFP_MOVABLE flag here only makes page allocation from non- movable zones, but doesn't necessarily prevent page from being migrated. My first glance is you need to implement either a_ops->migrate_folio() or just get_page() after faulting in the page to prevent. So I think the comment also needs improvement -- IMHO we can just call out currently those pages cannot be migrated and swapped, which is clearer (and the latter justifies mapping_set_unevictable() clearly).
