> On 12/15/2016 04:48 PM, Li, Liang Z wrote: > >>> It seems we leave too many bit for the pfn, and the bits leave for > >>> length is not enough, How about keep 45 bits for the pfn and 19 bits > >>> for length, 45 bits for pfn can cover 57 bits physical address, that > >>> should be > >> enough in the near feature. > >>> What's your opinion? > >> I still think 'order' makes a lot of sense. But, as you say, 57 bits > >> is enough for > >> x86 for a while. Other architectures.... who knows? > > Thinking about this some more... There are really only two cases that > matter: 4k pages and "much bigger" ones. > > Squeezing each 4k page into 8 bytes of metadata helps guarantee that this > scheme won't regress over the old scheme in any cases. For bigger ranges, 8 > vs 16 bytes means *nothing*. And 16 bytes will be as good or better than > the old scheme for everything which is >4k. > > How about this: > * 52 bits of 'pfn', 5 bits of 'order', 7 bits of 'length' > * One special 'length' value to mean "actual length in next 8 bytes" > > That should be pretty simple to produce and decode. We have two record > sizes, but I think it is manageable. It works, Now that we intend to use another 8 bytes for length Why not: Use 52 bits for 'pfn', 12 bits for 'length', when the 12 bits is not long enough for the 'length' Set the 'length' to a special value to indicate the "actual length in next 8 bytes". That will be much more simple. Right? Liang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
