On Thu, 20 Oct 2016 14:59:11 -0200 Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Thu, Oct 20, 2016 at 05:41:47PM +0200, Igor Mammedov wrote: > > On Thu, 20 Oct 2016 13:15:31 -0200 > > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > > > On Thu, Oct 20, 2016 at 04:17:35PM +0200, Igor Mammedov wrote: > > > > On Thu, 20 Oct 2016 11:47:18 -0200 > > > > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > > > > > > > On Thu, Oct 20, 2016 at 09:33:53PM +0800, Haozhong Zhang wrote: > > > > > > On 10/20/16 11:21 -0200, Eduardo Habkost wrote: > > > > > > > On Thu, Oct 20, 2016 at 02:34:12PM +0200, Igor Mammedov wrote: > > > > > > > > > > > > > > > On Thu, 20 Oct 2016 14:13:01 +0800 > > > > > > > > Haozhong Zhang <haozhong.zh...@intel.com> wrote: > > > > > > > > > > > > > > > > > If a file is used as the backend of memory-backend-file and > > > > > > > > > its size is > > > > > > > > > not identical to the property 'size', the file will be > > > > > > > > > truncated. For a > > > > > > > > > file used as the backend of vNVDIMM, its data is expected to > > > > > > > > > be > > > > > > > > > persistent and the truncation may corrupt the existing data. > > > > > > > > > > > > > > > > > I wonder if it's possible just skip 'size' property in your > > > > > > > > case instead > > > > > > > > 'notrunc' property. That way if size is not present one'd get > > > > > > > > actual size > > > > > > > > using get_file_size() and set 'size' to it? > > > > > > > > And if 'size' is provided and 'size' != file_size then error > > > > > > > > out. > > > > > > > > > > > > > > I think it is valid to start with a zero-size file and then let > > > > > > > QEMU extend it. > > > > > > > > > > > > For vNVDIMM, extending from zero-size file can be valid when a file > > > > > > is > > > > > > first used. However, it's not valid for the second and following use > > > > > > of the same file. > > > > > > > > > > > > > But I agree we should: 1) make 'size' optional as > > > > > > > you suggested; 2) never truncate the file to a smaller size. > > > > > > > > > > > > > > > > > > > I will add another patch for this. Is there any way in QEMU to > > > > > > decide > > > > > > whether a memory-backend-file object is used for vNVDIMM when the > > > > > > object is being created? Or 'size' can be optional for all kinds of > > > > > > usages? > > > > > > > > > > I believe 'size' can be optional for all usage, because at the > > > > > moment the memory allocation code asks the backend for a memory > > > > > region, it is supposed to know desired RAM size from the frontend > > > > > configuration (-numa, -m, or "size" property of pc-dimm). > > > > > > > > nope, currently the size propagates other way around > > > > from back-end to front-end and not backwards > > > > > > I'd say that this is a bug. Frontend size is guest ABI and > > > shouldn't be overridden by backend configuration if it's > > > explicitly set. > > frontend.size is always <= backend.size > > > > allocation specified when backend is created (-object/object_add) > > and front end size if needed/used is <= backend size > > > > so far code followed this design. > > This would work, but it doesn't happen in the case of -numa: > > $ ./x86_64-softmmu/qemu-system-x86_64 \ > -object memory-backend-file,id=mem0,mem-path=/tmp/mempath,size=2G \ > -numa node,size=1G,memdev=mem0 -m 1G > qemu-system-x86_64: total memory for NUMA nodes (0x80000000) should equal > RAM size (0x40000000) > > That's a bug we need to fix. it's mismatch between option "-m 1G" and sum of memory provided by options "-numa node,memdev=mem0 -object memory-backend-file,id=mem0,mem-path=/tmp/mempath,size=2G" Adding -numa 'size=1G' is a bug in above example as it's not supported option, but parse_numa somehow silently ignores it instead of failing. Allowing to map only 1G RAM of provided by backend 2G is kind of nonsense. Currently for pc-dim devices we allow 1:1 mapping only and initial memory falls into the same category, if we consider conversion of initial memory to set of pc-dimm devices then we shouldn't allow to do partial mapping for '-numa memdev' either. if we convert current numa memory mapping it pc-dimm terms it would look like: -object memory-backend-file,id=mem0,mem-path=/tmp/mempath,size=G -device pc-dimm,memdev=mem0,node=0 ... and we could drop/obsolete "-m SIZE -numa [mem|memdev]... CLI options
