On Thu, Feb 07, 2019 at 11:16:05PM +0800, Yi Zhang wrote: > On 2019-02-06 at 13:29:37 -0500, Michael S. Tsirkin wrote: > > On Thu, Feb 07, 2019 at 01:27:29AM +0800, Zhang, Yi wrote: > > > From: Zhang Yi <yi.z.zh...@linux.intel.com> > > > > > > Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com> > > > --- > > > docs/nvdimm.txt | 25 ++++++++++++++++++++++--- > > > qemu-options.hx | 4 ++++ > > > 2 files changed, 26 insertions(+), 3 deletions(-) > > > > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > > > index 5f158a6..e2bf89f 100644 > > > --- a/docs/nvdimm.txt > > > +++ b/docs/nvdimm.txt > > > @@ -143,9 +143,28 @@ Guest Data Persistence > > > ---------------------- > > > > > > Though QEMU supports multiple types of vNVDIMM backends on Linux, > > > -currently the only one that can guarantee the guest write persistence > > > -is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to > > > -which all guest access do not involve any host-side kernel cache. > > > +the only backend that can guarantee the guest write persistence is: > > > + > > > +A. DAX device (e.g., /dev/dax0.0, ) or > > > +B. DAX file(mounted with dax option) > > > + > > > +both are from the real NVDIMM device, all guest access do not > > > +involve any host-side kernel cache. > > > > I'm not sure - what do above 2 lines mean? > > That cache must not be used if persistence is desired? > same meaning of direct mapping of pmem, > Ah, Maybe better to change to: > "both are backend from the real NVDIMM device, which supportting direct > mapping of persistent memory." ?
Yes but typos aside it is still unclear - what is this? An extra condition when persistence is guaranteed? > > > > > + > > > +When using B (A file supporting direct mapping of persistent memory) > > > +as a backend, write persistence is guaranteed if the host kernel has > > > +support for the MAP_SYNC flag in the mmap system call (available > > > +since Linux 4.15 and on certain distro kernels) and additionally > > > +both 'pmem' and 'share' flags are set to 'on' on the backend. > > > + > > > +If these conditions are not satisfied i.e. if either 'pmem' or 'share' > > > +are not set, if the backend file does not support DAX or if MAP_SYNC > > > +is not supported by the host kernel, write persistence is not > > > +guaranteed after a system crash. For compatibility reasons, these > > > +conditions are silently ignored if not satisfied. Currently, no way > > > +is provided to test for them. > > > +For more details, please reference mmap(2) man page: > > > +http://man7.org/linux/man-pages/man2/mmap.2.html. > > > > > > When using other types of backends, it's suggested to set 'unarmed' > > > option of '-device nvdimm' to 'on', which sets the unarmed flag of the > > > diff --git a/qemu-options.hx b/qemu-options.hx > > > index 08f8516..0cd41f4 100644 > > > --- a/qemu-options.hx > > > +++ b/qemu-options.hx > > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel > > > NVDIMM). > > > If @option{pmem} is set to 'on', QEMU will take necessary operations to > > > guarantee the persistence of its own writes to @option{mem-path} > > > (e.g. in vNVDIMM label emulation and live migration). > > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure > > > > should be > > which ensures > > > > > +the file metadata is in sync to @option{mem-path} > > > > > > should be > > for @option{mem-path} > > > > > in case of host crash > > > +or a power failure. MAP_SYNC requires support from both the host kernel > > > +(since Linux kernel 4.15) and @option{mem-path} > > > > > > should be > > and the filesystem of @option{mem-path} > Thanks, will update it. > > > > > (only files supporting DAX). > > > > > > @item -object > > > memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} > > > > > > -- > > > 2.7.4
