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 02A17C3A59E for ; Wed, 21 Aug 2019 12:18:08 +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 CB4DC2064A for ; Wed, 21 Aug 2019 12:18:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB4DC2064A 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]:47878 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0PZ1-0004oQ-0b for qemu-devel@archiver.kernel.org; Wed, 21 Aug 2019 08:18:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34640) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0PXn-0004FG-7k for qemu-devel@nongnu.org; Wed, 21 Aug 2019 08:16:52 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i0PXl-00045i-8V for qemu-devel@nongnu.org; Wed, 21 Aug 2019 08:16:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56008) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i0PXj-000438-B8 for qemu-devel@nongnu.org; Wed, 21 Aug 2019 08:16:49 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 66FD43083362; Wed, 21 Aug 2019 12:16:45 +0000 (UTC) Received: from dhcp201-121.englab.pnq.redhat.com (ovpn-116-177.sin2.redhat.com [10.67.116.177]) by smtp.corp.redhat.com (Postfix) with ESMTP id 639012B0E7; Wed, 21 Aug 2019 12:16:28 +0000 (UTC) From: Pankaj Gupta To: qemu-devel@nongnu.org Date: Wed, 21 Aug 2019 17:46:24 +0530 Message-Id: <20190821121624.5382-1-pagupta@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Wed, 21 Aug 2019 12:16:45 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v3] 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: pagupta@redhat.com, david@redhat.com, cohuck@redhat.com, lcapitulino@redhat.com, mst@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" 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 --- v3->v3 - Text format fixes - Cornerlia 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..e77881b26f --- /dev/null +++ b/docs/virtio-pmem.rst @@ -0,0 +1,75 @@ + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +QEMU virtio pmem +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + + This document explains the setup and usage of the virtio pmem device + which is available since QEMU v4.1.0. + + The virtio pmem device is a paravirtualized persistent memory device + on regular (i.e non-NVDIMM) storage. + +Usecase +-------- + + Virtio pmem allows to bypass the guest page cache and directly use + host page cache. 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 + persist the guest writes as there are no defined semantics in the devi= ce + 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=3Dmem1,share,mem-path=3D./virtio_pmem.i= mg,size=3D4G + -device virtio-pmem-pci,memdev=3Dmem1,id=3Dnv1 + + where: + - "object memory-backend-file,id=3Dmem1,share,mem-path=3D, siz= e=3D" + creates a backend file with the specified size. + + - "device virtio-pmem-pci,id=3Dnvdimm1,memdev=3Dmem1" creates a virti= o pmem + pci device whose storage is provided by above memory backend device= . + + Multiple virtio pmem devices can be created if multiple pairs of "-obj= ect" + 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'. + +For example, the following commands add another 4GB virtio pmem device t= o +the guest: + + (qemu) object_add memory-backend-file,id=3Dmem2,share=3Don,mem-path=3Dv= irtio_pmem2.img,size=3D4G + (qemu) device_add virtio-pmem-pci,id=3Dvirtio_pmem2,memdev=3Dmem2 + +Guest Data Persistence +---------------------- + + Guest data persistence on non-NVDIMM requires guest userspace applicati= ons + to perform fsync/msync. This is different from a real nvdimm backend wh= ere + 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 prov= ides + 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. --=20 2.21.0 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 D6239C4CEC9 for ; Tue, 17 Sep 2019 15:17:11 +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 AB63721881 for ; Tue, 17 Sep 2019 15:17:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB63721881 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]:47168 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iAFE6-0006ks-DT for qemu-devel@archiver.kernel.org; Tue, 17 Sep 2019 11:17:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60255) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iAF8S-0002r1-JP for qemu-devel@nongnu.org; Tue, 17 Sep 2019 11:11:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iAF8R-0000Vt-AX for qemu-devel@nongnu.org; Tue, 17 Sep 2019 11:11:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44306) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iAF8R-0000Ve-1q for qemu-devel@nongnu.org; Tue, 17 Sep 2019 11:11:19 -0400 Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4A0DD8553D for ; Tue, 17 Sep 2019 15:11:18 +0000 (UTC) Received: by mail-qk1-f200.google.com with SMTP id b67so4582009qkc.1 for ; Tue, 17 Sep 2019 08:11:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Z+GrB4OsuKWsPCn93GzyHPdMpDZ0x8xOsHVIaXoGtYw=; b=etmGLb0Lyb0BFK6lJ0yyzxF4RUxcD3V6z8ahoNhjVgJFfS06w6TAGwM0A4/IQQp42C /y5o8HEai7aSe6OFz9jnBLJCOmOGgPnDSEHoVdFTC3V/+tX9mvOXEXQRly1jW4GEQQ1z jtysuZFA2Lum5z2A7sTvlhzurllSzHvGzqYyiOdIbsL+RsQWA8zpSEe5YLJqNvIcg7du hpyKQVysMXZxKOXhU4l9crYgmanFXpTAfSuCfWD66me8wQ7jQtg6tmXCPPVIzZ13/K28 2hmU6hmGaokBXW+5y9d8wtvb9ocJLwTzqnjCx4usEwxU1KIZaNtrdnyKwzbb1zZdcplp GAng== X-Gm-Message-State: APjAAAWk9VmTnppZOc3c5QSJSXMRSRqIReyaw7dn/89AjgT2UdwbSo1p ykhdunlmfSyJn/puaHSSycVsuz58feCVnuRRwNC9WQZOQ5t8Rgt74AVnyzryOw0NQG0cO10FmDO PKaGi3C7pSL11FWk= X-Received: by 2002:aed:208e:: with SMTP id 14mr4098951qtb.199.1568733077302; Tue, 17 Sep 2019 08:11:17 -0700 (PDT) X-Google-Smtp-Source: APXvYqytwd4w7rUw8gmpUNTcX9Ba+UYBFdr1yNI9tXtx1sByE8efBh/Q1slnfHa8u4uOhnDEUGcaZg== X-Received: by 2002:aed:208e:: with SMTP id 14mr4098923qtb.199.1568733077094; Tue, 17 Sep 2019 08:11:17 -0700 (PDT) Received: from redhat.com (bzq-79-176-40-226.red.bezeqint.net. [79.176.40.226]) by smtp.gmail.com with ESMTPSA id v5sm1529227qtk.66.2019.09.17.08.11.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Sep 2019 08:11:16 -0700 (PDT) Date: Tue, 17 Sep 2019 11:11:13 -0400 From: "Michael S. Tsirkin" To: qemu-devel@nongnu.org Message-ID: <20190821121624.5382-1-pagupta@redhat.com> References: <20190917151011.24588-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline In-Reply-To: <20190917151011.24588-1-mst@redhat.com> X-Mailer: git-send-email 2.22.0.678.g13338e74b8 X-Mutt-Fcc: =sent X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 09/10] 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: Peter Maydell , Cornelia Huck , Pankaj Gupta Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190917151113.bPpt7GYbdbtvLOpN3KQ6aOn_sXRojXyHFTvGi4BOBlo@z> From: Pankaj Gupta 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 Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- 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..e77881b26f --- /dev/null +++ b/docs/virtio-pmem.rst @@ -0,0 +1,75 @@ + +======================== +QEMU virtio pmem +======================== + + This document explains the setup and usage of the virtio pmem device + which is available since QEMU v4.1.0. + + The virtio pmem device is a paravirtualized persistent memory device + on regular (i.e non-NVDIMM) storage. + +Usecase +-------- + + Virtio pmem allows to bypass the guest page cache and directly use + host page cache. 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 + 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 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'. + +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 applications + to 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. -- MST