On 2018-12-19 at 10:59:10 -0500, Michael S. Tsirkin wrote: > On Wed, Dec 19, 2018 at 05:10:18PM +0800, Yi Zhang wrote: > > > > + > > > > + - 'sync' option of memory-backend-file is not 'off', and > > > > + > > > > + - 'share' option of memory-backend-file is 'on'. > > > > + > > > > + - 'pmem' option of memory-backend-file is 'on' > > > > + > > > > > > Wait isn't this what pmem was supposed to do? > > > Doesn't it mean "persistent memory"? > > pmem is a option for memory-backend-file, user should know the backend > > is in host persistent memory, with this flags on, while there is a host > > crash > > or a power failures. > > > > [1] Qemu will take necessary operations to guarantee the persistence. > > https://patchwork.ozlabs.org/cover/944749/ > > > > [2] Host kernel also take opretions to consistent filesystem metadata. > > Add MAP_SYNC flags. > > OK so I'm a user. Can you educate me please? We suppose an administrator should know it, what is the back-end region coming from, is it persistent? what is the font-end device is? a volatile dimm or an nonvolatile dimm? then they can choice put the pmem=on[off] and sync=on[off]. If he didn't, we encourage that don't set these 2 flags.
> When should MAP_SYNC not > be set? Are there any disadvantages (e.g. performance?)? Not only the performance, sometimes like the front-end device is an volatile ram, we don't wanna set such option although the backend is a novolatile memory, if power lose, all of thing should lose in this ram. > > -- > MST >
