> > Yes, this indeed could be a problem for some configurations. I will > > add your comment to the commit log of one of the patches. > > It sounds like there is some inherent tension here, breaking THP's > when doing pin_user_pages() is a really nasty thing to do. DMA > benefits greatly from THP. > > I know nothing about ZONE_MOVABLE, is this auto-setup or an admin > option? If the result of this patch is standard systems can no longer > pin > 80% of their memory I have some regression concerns.. ZONE_MOVABLE can be configured via kernel parameter, or when memory nodes are onlined after hot-add; so this is something that admins configure. ZONE_MOVABLE is designed to gurantee memory hot-plug functionality, and not availability of THP, however, I did not know about the use case where some admins might configure ZONE_MOVABLE to increase availability of THP because pages are always migratable in them. The thing is, if we fragment ZONE_MOVABLE by pinning pages in it, the availability of THP also suffers. We can migrate pages in ZONE_NORMAL, just not guaranteed, so we can create THP in ZONE_NORMAL as well, which is the usual case.
