On Fri, May 11, 2012 at 7:29 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: > On Fri, May 11, 2012 at 6:59 PM, KOSAKI Motohiro > <kosaki.motohiro@xxxxxxxxx> wrote: >>> My point is this ioctl will be restricted to one user (Xserver if i >>> understand) and only this user, there is no fork in it so no need to >>> worry about fork, just setting the vma as locked will be enough. >>> >>> But i don't want people reading this driver suddenly think that what >>> it's doing is ok, it's not, it's hack and can never make to work >>> properly on a general case, that's why it needs a big comment stating, >>> stressing that. I just wanted to make sure Inki and Kyungmin >>> understood that this kind of ioctl should be restricted to carefully >>> selected user and that there is no way to make it general or reliable >>> outside that. >> >> >> first off, I'm not drm guy and then I don't intend to insist you. but if >> application don't use fork, get_user_pages() has no downside. I guess we >> don't need VM_LOCKED hack. >> >> but again, up to drm folks. > > You need the VM_LOCKED hack to mare sure that the xorg vma still point > to the same page, afaict with get_user_pages pages can be migrated out > of the anonymous vma so the vma might point to new page, while old > page are still in use by the gpu and not recycle until their refcount > drop to 0. afaik, get_user_pages() prevent page migration. (see migrate_page_move_mapping). but mlock doesn't. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>