On Mon, Apr 07, 2014 at 07:28:54PM +0100, Mel Gorman wrote: > > > I didn't bother spelling it out in case I gave the impression that I was > > > blaming Xen for the problem. As the bit is now changes, does it help > > > the Xen problem or cause another collision of some sort? There is no > > > guarantee _PAGE_NUMA will remain as bit 62 but at worst it'll use bit 11 > > > and NUMA_BALANCING will depend in !KMEMCHECK. > > > > Fwiw, we're using bit 11 for soft-dirty tracking, so i really hope worst case > > never happen. (At the moment I'm trying to figure out if with this set > > it would be possible to clean up ugly macros in pgoff_to_pte for 2 level pages). > > I had considered the soft-dirty tracking usage of the same bit. I thought I'd > be able to swizzle around it or a further worst case of having soft-dirty and > automatic NUMA balancing mutually exclusive. Unfortunately upon examination > it's not obvious how to have both of them share a bit and I suspect any > attempt to will break CRIU. In my current tree, NUMA_BALANCING cannot be > set if MEM_SOFT_DIRTY which is not particularly satisfactory. Next on the > list is examining if _PAGE_BIT_IOMAP can be used. Thanks for info, Mel! It seems indeed if no more space left on x86-64 (in the very worst case which I still think won't happen anytime soon) we'll have to make them mut. exclusive. But for now (with 62 bit used for numa) they can live together, right? -- 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>