From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:60034) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grv62-0007l5-Mk for qemu-devel@nongnu.org; Thu, 07 Feb 2019 20:36:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grv5u-0003vG-R5 for qemu-devel@nongnu.org; Thu, 07 Feb 2019 20:36:46 -0500 Received: from mga06.intel.com ([134.134.136.31]:33513) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1grv5p-0003sV-GL for qemu-devel@nongnu.org; Thu, 07 Feb 2019 20:36:40 -0500 Date: Fri, 8 Feb 2019 18:07:08 +0800 From: Yi Zhang Message-ID: <20190208100707.GA61978@tiger-server> References: <3497114cb20658d8b40837675dcac9c78c04a345.1549473586.git.yi.z.zhang@linux.intel.com> <20190206132538-mutt-send-email-mst@kernel.org> <20190207151604.GA56533@tiger-server> <20190207092914-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190207092914-mutt-send-email-mst@kernel.org> Subject: Re: [Qemu-devel] [PATCH V12 5/5] docs: Added MAP_SYNC documentation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, ehabkost@redhat.com, qemu-devel@nongnu.org, imammedo@redhat.com, dan.j.williams@intel.com On 2019-02-07 at 09:30:12 -0500, Michael S. Tsirkin wrote: > 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 > > > > > > > > Signed-off-by: Zhang Yi > > > > --- > > > > 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. Yes, A and B both based on the direct access for files/devices(no page 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 >