Il 15/03/2012 01:42, Richard Laager ha scritto: >> > It is worse in that we do not want the hardware parameters exposed to the >> > guest to change behind the scenes, except if you change the machine type >> > or if you use the default unversioned type. > You're saying that discard_granularity and discard_zeros_data need to be > properties of the machine type? If you start with that as a requirement, > I can see why you want to always report discard_granularity=512 & > discard_zeros_data=1. But that design has many downsides. I'm not > convinced that discard_granularity and discard_zeros_data need to be > properties of the machine type. Why do you feel that's necessary? What's > the harm in those properties changing across QEMU startups (i.e. guest > boots)?
Changing across guest boots is a minor problem, but changing across migration must be avoided at all costs. BTW, after this discussion I think we can instead report discard_granularity = 512 and discard_zeroes_data=0 and get most of the benefit, at least on file-backed storage. Paolo
