From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:39588) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1glSsP-0001e0-4o for qemu-devel@nongnu.org; Mon, 21 Jan 2019 01:16:06 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1glSo2-0004tk-9q for qemu-devel@nongnu.org; Mon, 21 Jan 2019 01:11:37 -0500 Received: from mga11.intel.com ([192.55.52.93]:42259) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1glSo0-0004rK-1F for qemu-devel@nongnu.org; Mon, 21 Jan 2019 01:11:32 -0500 Date: Mon, 21 Jan 2019 14:11:43 +0800 From: Yi Zhang Message-ID: <20190121061143.GB21562@tiger-server> References: <20190116103615-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190116103615-mutt-send-email-mst@kernel.org> Subject: Re: [Qemu-devel] [PATCH V9 6/6] 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, ehabkost@redhat.com, qemu-devel@nongnu.org, imammedo@redhat.com, dan.j.williams@intel.com On 2019-01-16 at 10:40:23 -0500, Michael S. Tsirkin wrote: > On Wed, Jan 16, 2019 at 04:11:16PM +0800, Zhang Yi wrote: > > Signed-off-by: Zhang Yi > > --- > > docs/nvdimm.txt | 21 ++++++++++++++++++++- > > qemu-options.hx | 4 ++++ > > 2 files changed, 24 insertions(+), 1 deletion(-) > > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > > index 5f158a6..565ba73 100644 > > --- a/docs/nvdimm.txt > > +++ b/docs/nvdimm.txt > > @@ -142,11 +142,30 @@ backend of vNVDIMM: > > Guest Data Persistence > > ---------------------- > > > > +vNVDIMM is designed and implemented to guarantee the guest data > > +persistence on the backends even on the host crash and power > > in case of a host crash or a power failure > > (be consistent) > > > +failures. However, there are still some requirements and limitations > > +as explained below. > > + > > Though QEMU supports multiple types of vNVDIMM backends on Linux, > > -currently the only one that can guarantee the guest write persistence > > +if MAP_SYNC is not supported by the host kernel and the backends, > > +the only backend 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. > > > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure > > which ensures > > > +filesystem metadata consistent > > consistency > > > even after a system crash or power > > a power > > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU > > +also requires: > > + > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or > > + xfs file system mounted with '-o dax', > > + > > + - 'share' option of memory-backend-file is 'on'. > > why does share need to be on? According to mmap(2) man page, MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type. I will add this to documentation, Thanks. > > > + > > + - 'pmem' option of memory-backend-file is 'on' > > + > > 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 > > guest NVDIMM region mapping structure. This unarmed flag indicates > > diff --git a/qemu-options.hx b/qemu-options.hx > > index 08f8516..545cb8a 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 > > +the file metadata is in sync to @option{mem-path} even on the host crash > > +and power failures. MAP_SYNC requires supports from both the host kernel > > requires support > > > +(since Linux kernel 4.15) and @option{mem-path} (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