From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45095) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZeFy-0004kN-QN for qemu-devel@nongnu.org; Wed, 19 Dec 2018 10:59:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gZeFk-0004q8-EF for qemu-devel@nongnu.org; Wed, 19 Dec 2018 10:59:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38184) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gZeFh-0004mI-Os for qemu-devel@nongnu.org; Wed, 19 Dec 2018 10:59:19 -0500 Date: Wed, 19 Dec 2018 10:59:10 -0500 From: "Michael S. Tsirkin" Message-ID: <20181219105555-mutt-send-email-mst@kernel.org> References: <5eb87eb9a389242772375dd52bd97c17564a0829.1545120100.git.yi.z.zhang@linux.intel.com> <20181218085249-mutt-send-email-mst@kernel.org> <20181219091017.GA35378@tiger-server> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219091017.GA35378@tiger-server> Subject: Re: [Qemu-devel] [PATCH V7 6/6] hostmem-file: add 'sync' option List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: peter.maydell@linaro.org, yu.c.zhang@linux.intel.com, ehabkost@redhat.com, imammedo@redhat.com, qemu-devel@nongnu.org, pbonzini@redhat.com, stefanha@redhat.com, crosthwaite.peter@gmail.com, richard.henderson@linaro.org, xiaoguangrong.eric@gmail.com On Wed, Dec 19, 2018 at 05:10:18PM +0800, Yi Zhang wrote: > > > + > > > + - 'sync' option of memory-backend-file is not 'off', and > > > + > > > + - 'share' option of memory-backend-file is 'on'. > > > + > > > + - 'pmem' option of memory-backend-file is 'on' > > > + > > > > Wait isn't this what pmem was supposed to do? > > Doesn't it mean "persistent memory"? > pmem is a option for memory-backend-file, user should know the backend > is in host persistent memory, with this flags on, while there is a host crash > or a power failures. > > [1] Qemu will take necessary operations to guarantee the persistence. > https://patchwork.ozlabs.org/cover/944749/ > > [2] Host kernel also take opretions to consistent filesystem metadata. > Add MAP_SYNC flags. OK so I'm a user. Can you educate me please? When should MAP_SYNC not be set? Are there any disadvantages (e.g. performance?)? -- MST