From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: KVM "fake DAX" device flushing Date: Thu, 11 May 2017 17:35:54 -0400 Message-ID: <1494538554.20270.33.camel@redhat.com> References: <1494431760-6455-1-git-send-email-pagupta@redhat.com> <20170511181703.GC8701@stefanha-x1.localdomain> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-+amXkFCaHJpXiKQp2Jba" Cc: Pankaj Gupta , KVM list , qemu-devel@nongnu.org, Paolo Bonzini , kwolf@redhat.com, Haozhong Zhang , Xiao Guangrong To: Dan Williams , Stefan Hajnoczi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60716 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755606AbdEKVgF (ORCPT ); Thu, 11 May 2017 17:36:05 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: --=-+amXkFCaHJpXiKQp2Jba Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2017-05-11 at 12:15 -0700, Dan Williams wrote: > On Thu, May 11, 2017 at 11:17 AM, Stefan Hajnoczi m> wrote: > > On Wed, May 10, 2017 at 09:26:00PM +0530, Pankaj Gupta wrote: > > > We are sharing initial project proposal for > > > 'KVM "fake DAX" device flushing' project for feedback. > > > Got the idea during discussion with 'Rik van Riel'. > >=20 > > CCing NVDIMM folks. > >=20 > > >=20 > > > Also, request answers to 'Questions' section. > > >=20 > > > Abstract : > > > ---------- > > > Project idea is to use fake persistent memory with direct > > > access(DAX) in virtual machines. Overall goal of project > > > is to increase the number of virtual machines that can be > > > run on a physical machine, in order to increase the density > > > of customer virtual machines. > > >=20 > > > The idea is to avoid the guest page cache, and minimize the > > > memory footprint of virtual machines. By presenting a disk > > > image as a nvdimm direct access (DAX) memory region in a > > > virtual machine, the guest OS can avoid using page cache > > > memory for most file accesses. >=20 > How is this different than the solution that Clear Containers came up > with? >=20 > https://lwn.net/Articles/644675/ Clear Containers uses MAP_PRIVATE with read-only images. This solution is about making read-write images work. When a program in the guest calls fsync, we need to ensure the data has actually hit the disk on the host side before fsync returns. --=20 All rights reversed --=-+amXkFCaHJpXiKQp2Jba Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAABCAAGBQJZFNk6AAoJEM553pKExN6DT+AH+gIF4T1gWc98+Ah/IS62ohYZ 0BUevhwk7lNgtj0v65oH2MQTNrRbtL4rQ0WJ4crBlLCWi0/JAff1Z3W5qdPpHZrv 10yoIVyEiLTQHXfHjBjx0C41ZOFcMqga122bZpspLWhOiuE0ozqad+N4dMHe3oD1 iXjCFWN/KhzDiFhEQxtv0AtSWiUFVb5vgf2xNuK97xkwJv8SragYtmbBDqZ1Bt3X iG3npLQNIOM8tJfnhm+z2G0xA2Rf683K4zTzGg3+0+dN3xBwSI84x8cxvNdEFCoG IvXd7ruehWyldzCJjbdAGsXZpRSC19pRWkR4xbY50Bvhcc7iYN5AKBUR6CP4/us= =5oa2 -----END PGP SIGNATURE----- --=-+amXkFCaHJpXiKQp2Jba-- From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44012) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1d8vkk-0007xN-9p for qemu-devel@nongnu.org; Thu, 11 May 2017 17:36:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1d8vkf-0006zw-Vu for qemu-devel@nongnu.org; Thu, 11 May 2017 17:36:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47216) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1d8vkf-0006z1-MV for qemu-devel@nongnu.org; Thu, 11 May 2017 17:36:01 -0400 Message-ID: <1494538554.20270.33.camel@redhat.com> From: Rik van Riel Date: Thu, 11 May 2017 17:35:54 -0400 In-Reply-To: References: <1494431760-6455-1-git-send-email-pagupta@redhat.com> <20170511181703.GC8701@stefanha-x1.localdomain> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-+amXkFCaHJpXiKQp2Jba" Mime-Version: 1.0 Subject: Re: [Qemu-devel] KVM "fake DAX" device flushing List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Dan Williams , Stefan Hajnoczi Cc: Pankaj Gupta , KVM list , qemu-devel@nongnu.org, Paolo Bonzini , kwolf@redhat.com, Haozhong Zhang , Xiao Guangrong --=-+amXkFCaHJpXiKQp2Jba Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2017-05-11 at 12:15 -0700, Dan Williams wrote: > On Thu, May 11, 2017 at 11:17 AM, Stefan Hajnoczi m> wrote: > > On Wed, May 10, 2017 at 09:26:00PM +0530, Pankaj Gupta wrote: > > > We are sharing initial project proposal for > > > 'KVM "fake DAX" device flushing' project for feedback. > > > Got the idea during discussion with 'Rik van Riel'. > >=20 > > CCing NVDIMM folks. > >=20 > > >=20 > > > Also, request answers to 'Questions' section. > > >=20 > > > Abstract : > > > ---------- > > > Project idea is to use fake persistent memory with direct > > > access(DAX) in virtual machines. Overall goal of project > > > is to increase the number of virtual machines that can be > > > run on a physical machine, in order to increase the density > > > of customer virtual machines. > > >=20 > > > The idea is to avoid the guest page cache, and minimize the > > > memory footprint of virtual machines. By presenting a disk > > > image as a nvdimm direct access (DAX) memory region in a > > > virtual machine, the guest OS can avoid using page cache > > > memory for most file accesses. >=20 > How is this different than the solution that Clear Containers came up > with? >=20 > https://lwn.net/Articles/644675/ Clear Containers uses MAP_PRIVATE with read-only images. This solution is about making read-write images work. When a program in the guest calls fsync, we need to ensure the data has actually hit the disk on the host side before fsync returns. --=20 All rights reversed --=-+amXkFCaHJpXiKQp2Jba Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAABCAAGBQJZFNk6AAoJEM553pKExN6DT+AH+gIF4T1gWc98+Ah/IS62ohYZ 0BUevhwk7lNgtj0v65oH2MQTNrRbtL4rQ0WJ4crBlLCWi0/JAff1Z3W5qdPpHZrv 10yoIVyEiLTQHXfHjBjx0C41ZOFcMqga122bZpspLWhOiuE0ozqad+N4dMHe3oD1 iXjCFWN/KhzDiFhEQxtv0AtSWiUFVb5vgf2xNuK97xkwJv8SragYtmbBDqZ1Bt3X iG3npLQNIOM8tJfnhm+z2G0xA2Rf683K4zTzGg3+0+dN3xBwSI84x8cxvNdEFCoG IvXd7ruehWyldzCJjbdAGsXZpRSC19pRWkR4xbY50Bvhcc7iYN5AKBUR6CP4/us= =5oa2 -----END PGP SIGNATURE----- --=-+amXkFCaHJpXiKQp2Jba--