On Tue, Apr 01, 2014 at 11:43:11AM -0700, Linus Torvalds wrote: > On Tue, Apr 1, 2014 at 11:18 AM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote: > > > > I don't think it's sufficient to avoid collisions with bits used only > > with P=0. The original value of this bit must be retained when the > > _PAGE_NUMA bit is set/cleared. > > > > Bit 7 is PAT[2] and whilst Linux currently sets up the PAT such that > > PAT[2] is a 'don't care', there has been talk up adjusting the PAT to > > include more types. So I'm not sure it's a good idea to use bit 7. > > > > What's wrong with using e.g., bit 62? And not supporting this NUMA > > rebalancing feature on 32-bit non-PAE builds? > > Sounds good to me, but it's not available in 32-bit PAE. The high bits > are all reserved, afaik. > > But you'd have to be insane to care about NUMA balancing on 32-bit, > even with PAE. So restricting it to x86-64 and using the high bits (I > think bits 52-62 are all available to SW) sounds fine to me. > > Same goes for soft-dirty. I think it's fine if we say that you won't > have soft-dirty with a 32-bit kernel. Even with PAE. Well, at the moment we use soft-dirty for x86-64 only in criu but there were plans to implement complete 32bit support as well. While personally I don't mind dropping soft-dirty for non x86-64 case, I would like to hear Pavel's opinion, Pavel? (n.b, i'm still working on cleaning up _page bits, it appeared to be harder than I've been expecting). -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>