From patchwork Wed Jan 16 08:11:16 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Zhang, Yi" X-Patchwork-Id: 10765481 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9932A17FB for ; Wed, 16 Jan 2019 08:14:11 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8AAFF2AB8C for ; Wed, 16 Jan 2019 08:14:11 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 7EC922ABD2; Wed, 16 Jan 2019 08:14:11 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 1E7432ABCC for ; Wed, 16 Jan 2019 08:14:11 +0000 (UTC) Received: from localhost ([127.0.0.1]:44350 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjgKw-0007RM-Bp for patchwork-qemu-devel@patchwork.kernel.org; Wed, 16 Jan 2019 03:14:10 -0500 Received: from eggs.gnu.org ([209.51.188.92]:48643) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjgI2-0005CM-Pn for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:11:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gjgHz-0007Pm-GJ for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:11:09 -0500 Received: from mga06.intel.com ([134.134.136.31]:20110) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gjgHx-0007JT-Am for qemu-devel@nongnu.org; Wed, 16 Jan 2019 03:11:07 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Jan 2019 00:11:00 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,485,1539673200"; d="scan'208";a="117115289" Received: from linux.intel.com ([10.54.29.200]) by fmsmga008.fm.intel.com with ESMTP; 16 Jan 2019 00:11:00 -0800 Received: from dazhang1-ssd.sh.intel.com (dazhang1-ssd.sh.intel.com [10.239.48.128]) by linux.intel.com (Postfix) with ESMTP id 1CAEB5800C6; Wed, 16 Jan 2019 00:10:57 -0800 (PST) From: Zhang Yi To: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, mst@redhat.com, ehabkost@redhat.com Date: Wed, 16 Jan 2019 16:11:16 +0800 Message-Id: X-Mailer: git-send-email 2.7.4 In-Reply-To: References: X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.31 Subject: [Qemu-devel] [PATCH V9 6/6] docs: Added MAP_SYNC documentation X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: imammedo@redhat.com, dan.j.williams@intel.com, qemu-devel@nongnu.org, Zhang Yi Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP Signed-off-by: Zhang Yi --- docs/nvdimm.txt | 21 ++++++++++++++++++++- qemu-options.hx | 4 ++++ 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 5f158a6..565ba73 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -142,11 +142,30 @@ backend of vNVDIMM: Guest Data Persistence ---------------------- +vNVDIMM is designed and implemented to guarantee the guest data +persistence on the backends even on the host crash and power +failures. However, there are still some requirements and limitations +as explained below. + Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one that can guarantee the guest write persistence +if MAP_SYNC is not supported by the host kernel and the backends, +the only backend that can guarantee the guest write persistence is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to which all guest access do not involve any host-side kernel cache. +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure +filesystem metadata consistent even after a system crash or power +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU +also requires: + + - the backend is a file supporting DAX, e.g., a file on an ext4 or + xfs file system mounted with '-o dax', + + - 'share' option of memory-backend-file is 'on'. + + - 'pmem' option of memory-backend-file is 'on' + When using other types of backends, it's suggested to set 'unarmed' option of '-device nvdimm' to 'on', which sets the unarmed flag of the guest NVDIMM region mapping structure. This unarmed flag indicates diff --git a/qemu-options.hx b/qemu-options.hx index 08f8516..545cb8a 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM). If @option{pmem} is set to 'on', QEMU will take necessary operations to guarantee the persistence of its own writes to @option{mem-path} (e.g. in vNVDIMM label emulation and live migration). +Also, we will map the backend-file with MAP_SYNC flag, which can ensure +the file metadata is in sync to @option{mem-path} even on the host crash +and power failures. MAP_SYNC requires supports from both the host kernel +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX). @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}