From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 42BD8C3A59E for ; Wed, 21 Aug 2019 11:36:37 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1806422CF7 for ; Wed, 21 Aug 2019 11:36:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1806422CF7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47222 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0Oup-0006ZD-MJ for qemu-devel@archiver.kernel.org; Wed, 21 Aug 2019 07:36:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54640) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0Oja-0002kk-IP for qemu-devel@nongnu.org; Wed, 21 Aug 2019 07:25:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i0OjY-0000mA-Ss for qemu-devel@nongnu.org; Wed, 21 Aug 2019 07:24:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41022) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i0OjY-0000k3-FJ for qemu-devel@nongnu.org; Wed, 21 Aug 2019 07:24:56 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BEE0B3082128; Wed, 21 Aug 2019 11:24:54 +0000 (UTC) Received: from gondolin (dhcp-192-222.str.redhat.com [10.33.192.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id EF818194BE; Wed, 21 Aug 2019 11:24:42 +0000 (UTC) Date: Wed, 21 Aug 2019 13:24:40 +0200 From: Cornelia Huck To: Pankaj Gupta Message-ID: <20190821132440.066dfbba.cohuck@redhat.com> In-Reply-To: <20190821073630.2561-1-pagupta@redhat.com> References: <20190821073630.2561-1-pagupta@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 21 Aug 2019 11:24:54 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2] virtio pmem: user document X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mst@redhat.com, david@redhat.com, qemu-devel@nongnu.org, lcapitulino@redhat.com, stefanha@redhat.com, riel@surriel.com, nilal@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 21 Aug 2019 13:06:30 +0530 Pankaj Gupta wrote: > This patch documents the steps to use virtio pmem. > It also documents other useful information about > virtio pmem e.g use-case, comparison with Qemu NVDIMM > backend and current limitations. > > Signed-off-by: Pankaj Gupta > --- > v1->v2 > - Fixes on text format and 'Guest Data persistence' > section - Cornelia > > docs/virtio-pmem.rst | 75 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 75 insertions(+) > create mode 100644 docs/virtio-pmem.rst > > diff --git a/docs/virtio-pmem.rst b/docs/virtio-pmem.rst > new file mode 100644 > index 0000000000..0346e61674 > --- /dev/null > +++ b/docs/virtio-pmem.rst > @@ -0,0 +1,75 @@ > + > +======================== > +QEMU virtio pmem > +======================== > + > + This document explains the setup and usage of virtio pmem device s/virtio pmem device/the virtio pmem device/ > + which is available since QEMU v4.1.0. > + > + The virtio pmem is a paravirtualized persistent memory device on s/The virtio pmem/The virtio pmem device/ > + regular(i.e non-NVDIMM) storage. missing blank before '(' > + > +Usecase > +-------- > + > + Allows to bypass the guest page cache and directly use host page cache. "Virtio pmem allows to..." ? > + This reduces guest memory footprint as the host can make efficient > + memory reclaim decisions under memory pressure. > + > +o How does virtio-pmem compare to the nvdimm emulation supported by QEMU? > + > + NVDIMM emulation on regular(i.e. non-NVDIMM) host storage does not missing blank before '(' > + persist the guest writes as there are no defined semantics in the device > + specification. The virtio pmem device provides guest write persistence > + on non-NVDIMM host storage. > + > +virtio pmem usage > +----------------- > + > + A virtio pmem device backed by a memory-backend-file can be created on > + the QEMU command line as in the following example: > + > + -object memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G > + -device virtio-pmem-pci,memdev=mem1,id=nv1 > + > + where: > + - "object memory-backend-file,id=mem1,share,mem-path=, size=" > + creates a backend file of size on a mem-path. "a backend file with the specified size" ? > + > + - "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem > + pci device whose storage is provided by above memory backend device. > + > + Multiple virtio pmem devices can be created if multiple pairs of "-object" > + and "-device" are provided. > + > +Hotplug > +------- > + > +"Virtio pmem devices can be hotplugged via the QEMU monitor. First, the > +memory backing has to be added via 'object_add'; afterwards, the virtio > +pmem device can be added via 'device_add'." Please lose the '"' (copy/paste leftover, I presume? :) > + > +For example, the following commands add another 4GB virtio pmem device to > +the guest: > + > + (qemu) object_add memory-backend-file,id=mem2,share=on,mem-path=virtio_pmem2.img,size=4G > + (qemu) device_add virtio-pmem-pci,id=virtio_pmem2,memdev=mem2 > + > +Guest Data Persistence > +---------------------- > + > + Guest data persistence on non-NVDIMM requires guest userspace application to s/application/applications/ ? > + perform fsync/msync. This is different from a real nvdimm backend where no > + additional fsync/msync is required. This is to persist guest writes in host > + backing file which otherwise remains in host page cache and there is risk of > + losing the data in case of power failure. > + > + With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides > + a hint to application to perform fsync for write persistence. > + > +Limitations > +------------ > +- Real nvdimm device backend is not supported. > +- virtio pmem hotunplug is not supported. > +- ACPI NVDIMM features like regions/namespaces are not supported. > +- ndctl command is not supported. Only some nits from my side, otherwise looks good to me.