On Thu, Apr 06, 2017 at 06:53:09PM +0800, Haozhong Zhang wrote: > On 04/06/17 11:13 +0100, Stefan Hajnoczi wrote: > > On Fri, Mar 31, 2017 at 04:41:47PM +0800, Haozhong Zhang wrote: > > > > > > Add an boolean option 'flush-hint' to device 'nvdimm'. If it's on, a > > > flush hint address structure will be constructed for each nvdimm > > > device. > > > > Users should not need to set the flush hint option. NVDIMM > > configurations that persist data properly without Flush Hint Addresses > > shouldn't use them (for best performance). Configurations that rely on > > flush hints *must* use them to guarantee data integrity. > > It's for backwards compatibility, i.e. migrating a VM on QEMU w/o > flush hint support to another one w/ flush hint support. By using a > flush-hint option and making it disabled by default, users can ensure > both QEMU provide the same VM configuration.
I think QEMU should play a role in deciding whether to use Address Flush Hints or not. We should not require the user to set a sensible value. If they get it wrong then they may suffer data loss! Stefan
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