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Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option |
Date: |
Wed, 19 Dec 2018 22:42:07 -0500 |
On Thu, Dec 20, 2018 at 11:03:12AM +0800, Yi Zhang wrote:
> 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.
I am not sure how does above answer the questions. If I don't know,
neither will the hypothetical administrator. Looks like a better
interface is needed to make the choice on behalf of the user.
> >
> > --
> > MST
> >
- Re: [Qemu-devel] [PATCH V7 3/6] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap(), (continued)
[Qemu-devel] [PATCH V7 4/6] util/mmap-alloc: Switch the RAM_SYNC flags to OnOffAuto, Zhang Yi, 2018/12/18
[Qemu-devel] [PATCH V7 5/6] hostmem: add more information in error messages, Zhang Yi, 2018/12/18
[Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Zhang Yi, 2018/12/18
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Michael S. Tsirkin, 2018/12/18
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Yi Zhang, 2018/12/19
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Michael S. Tsirkin, 2018/12/19
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Yi Zhang, 2018/12/19
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Yi Zhang, 2018/12/20
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Michael S. Tsirkin, 2018/12/20
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Yi Zhang, 2018/12/20
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Michael S. Tsirkin, 2018/12/21
- Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option, Yi Zhang, 2018/12/24
Re: [Qemu-devel] [PATCH V7 0/6] nvdimm: support MAP_SYNC for memory-backend-file, Stefan Hajnoczi, 2018/12/18