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 65B83C433FF for ; Tue, 30 Jul 2019 12:06:09 +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 3557420693 for ; Tue, 30 Jul 2019 12:06:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3557420693 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]:60446 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hsQtM-0005lX-Hl for qemu-devel@archiver.kernel.org; Tue, 30 Jul 2019 08:06:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59428) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hsQsm-0004rA-VJ for qemu-devel@nongnu.org; Tue, 30 Jul 2019 08:05:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hsQsl-00019F-Jb for qemu-devel@nongnu.org; Tue, 30 Jul 2019 08:05:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34198) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hsQsl-00018p-Ad for qemu-devel@nongnu.org; Tue, 30 Jul 2019 08:05:31 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8A0F7B0CCB; Tue, 30 Jul 2019 12:05:30 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7C9F0605A8; Tue, 30 Jul 2019 12:05:30 +0000 (UTC) Received: from zmail21.collab.prod.int.phx2.redhat.com (zmail21.collab.prod.int.phx2.redhat.com [10.5.83.24]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 5A8A21806B01; Tue, 30 Jul 2019 12:05:30 +0000 (UTC) Date: Tue, 30 Jul 2019 08:05:29 -0400 (EDT) From: Pankaj Gupta To: Cornelia Huck Message-ID: <835647202.5426199.1564488329949.JavaMail.zimbra@redhat.com> In-Reply-To: <20190730114548.4ff4188b.cohuck@redhat.com> References: <20190730064658.27369-1-pagupta@redhat.com> <20190730114548.4ff4188b.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.116.177, 10.4.195.29] Thread-Topic: virtio pmem: user document Thread-Index: YB8Kh4j3lyLHqeerYOdlIJxC6YtgrA== X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 30 Jul 2019 12:05:30 +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] 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: aarcange@redhat.com, riel@surriel.com, mst@redhat.com, david@redhat.com, qemu-devel@nongnu.org, lcapitulino@redhat.com, stefanha@redhat.com, nilal@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > On Tue, 30 Jul 2019 12:16:57 +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 > > --- > > docs/virtio-pmem.txt | 65 ++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 65 insertions(+) > > create mode 100644 docs/virtio-pmem.txt > > > > diff --git a/docs/virtio-pmem.txt b/docs/virtio-pmem.txt > > Maybe make this ReST from the start? Should be trivial enough. o.k > > > new file mode 100644 > > index 0000000000..fc61eebb20 > > --- /dev/null > > +++ b/docs/virtio-pmem.txt > > @@ -0,0 +1,65 @@ > > + > > +QEMU virtio pmem > > +=================== > > + > > + This document explains the usage of virtio pmem device > > "setup and usage" ? o.k > > > + which is available since QEMU v4.1.0. > > + > > + The virtio pmem is paravirtualized persistent memory device > > "The virtio pmem device is a paravirtualized..." sure. > > > + on regular(non-NVDIMM) storage. > > + > > +Usecase > > +-------- > > + Allows to bypass the guest page cache and directly use host page cache. > > + This reduces guest memory footprint as host can make efficient memory > > s/as host/,as the host/ sure > > > + reclaim decisions under memory pressure. > > + > > +o How does virtio-pmem compare to the nvdimm emulation supported by QEMU? > > + > > + NVDIMM emulation on regular(non-NVDIMM) host storage does not persists > > s/regular(non-NVDIMM)/regular (i.e. non-NVDIMM)/ ? > s/persists/persist/ yes, to both. > > > + the guest writes as there are no defined semantecs in the device > > specification. > > s/semantecs/semantics/ ah...spell checker :( > > > + With virtio pmem device, guest write persistence on non-NVDIMM storage > > is > > + supported. > > "The virtio pmem device provides a way to support guest write > persistence on non-NVDIMM storage." ? > > > + > > +virtio pmem usage > > +----------------- > > + virtio pmem device is created with a memory-backend-file with the below > > + options: > > "A virtio pmem device backed by a memory-backend-file can be created on > the QEMU command line as in the following example:" ? o.k > > > + > > + -machine pc -m 8G,slots=$N,maxmem=$MAX_SIZE > > I'm not sure you should explicitly specify the machine type in this > example. I think it is fine to say that something is only supported on > a subset of machine types, but it should not make its way into an > example on how to configure a device and its backing. o.k > > Also, maybe fill in more concrete values here? Or split it into a part > specifying the syntax (where I'd use instead of $MAX_SIZE > etc.), and a more concrete example? o.k > > > + -object memory-backend-file,id=mem1,share,mem-path=$PATH,size=$SIZE > > + -device virtio-pmem-pci,memdev=mem1,id=nv1 > > + > > + where: > > + - "object > > memory-backend-file,id=mem1,share,mem-path=$PATH,size=$VIRTIO_PMEM_SIZE" > > + creates a backend storage of size $SIZE on a file $PATH. All > > + accesses to the virtio pmem device go to the file $PATH. > > + > > + - "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem > > + device whose storage is provided by above memory backend device. > > "a virtio pmem PCI device" ? o.k > > > + > > + Multiple virtio pmem devices can be created if multiple pairs of > > "-object" > > + and "-device" are provided. > > + > > +Hotplug > > +------- > > +Accomplished by two monitor commands "object_add" and "device_add". > > Hm... what about the following instead: > > "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'." o.k > > > + > > +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 than real nvdimm backend where no > > additional > > s/than/from a/ ? yes. > > > +fsync/msync is required for data persistence. > > Should we be a bit more verbose on what which guest applications are > supposed to do? I.e., how do they know they need to do fsync/msync, > when should they do it, and what are the consequences if they don't? o.k. > > > + > > +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. Thank you for the review. Best regards, Pankaj > > >