| Message ID | 20190422004849.26463-3-richardw.yang@linux.intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | support MAP_SYNC for memory-backend-file | expand |
On Mon, Apr 22, 2019 at 08:48:49AM +0800, Wei Yang wrote: > From: Zhang Yi <yi.z.zhang@linux.intel.com> > > Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com> > --- > docs/nvdimm.txt | 22 +++++++++++++++++++--- > qemu-options.hx | 5 +++++ > 2 files changed, 24 insertions(+), 3 deletions(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> > From: Zhang Yi <yi.z.zhang@linux.intel.com> > > Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com> > --- > docs/nvdimm.txt | 22 +++++++++++++++++++--- > qemu-options.hx | 5 +++++ > 2 files changed, 24 insertions(+), 3 deletions(-) > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > index 7231c2d78f..bcd1456e72 100644 > --- a/docs/nvdimm.txt > +++ b/docs/nvdimm.txt > @@ -144,9 +144,25 @@ 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) > + > +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 08749a3391..bdc74c0620 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -4233,6 +4233,11 @@ 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 ensures the > +file metadata is in sync 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 the filesystem of @option{mem-path} mounted > +with DAX option. > > @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} > > -- > 2.19.1 Looks good to me. Reviewed-by: Pankaj Gupta <pagupta@redhat.com> > > >
diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 7231c2d78f..bcd1456e72 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -144,9 +144,25 @@ 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) + +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 08749a3391..bdc74c0620 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4233,6 +4233,11 @@ 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 ensures the +file metadata is in sync 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 the filesystem of @option{mem-path} mounted +with DAX option. @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}