From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:41617) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hINEd-0007lO-4o for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hINEc-0003dg-0U for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:03 -0400 Received: from mga18.intel.com ([134.134.136.126]:34181) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hINEb-0003cj-Og for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:01 -0400 From: Wei Yang Date: Mon, 22 Apr 2019 08:48:49 +0800 Message-Id: <20190422004849.26463-3-richardw.yang@linux.intel.com> In-Reply-To: <20190422004849.26463-1-richardw.yang@linux.intel.com> References: <20190422004849.26463-1-richardw.yang@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH v14 2/2] docs: Added MAP_SYNC documentation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, mst@redhat.com, ehabkost@redhat.com, imammedo@redhat.com, dan.j.williams@intel.com, yi.z.zhang@linux.intel.com From: Zhang Yi Signed-off-by: Zhang Yi --- docs/nvdimm.txt | 22 +++++++++++++++++++--- qemu-options.hx | 5 +++++ 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 7231c2d78f..bcd1456e72 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -144,9 +144,25 @@ Guest Data Persistence ---------------------- Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one 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. +the only backend that can guarantee the guest write persistence is: + +A. DAX device (e.g., /dev/dax0.0, ) or +B. DAX file(mounted with dax option) + +When using B (A file supporting direct mapping of persistent memory) +as a backend, write persistence is guaranteed if the host kernel has +support for the MAP_SYNC flag in the mmap system call (available +since Linux 4.15 and on certain distro kernels) and additionally +both 'pmem' and 'share' flags are set to 'on' on the backend. + +If these conditions are not satisfied i.e. if either 'pmem' or 'share' +are not set, if the backend file does not support DAX or if MAP_SYNC +is not supported by the host kernel, write persistence is not +guaranteed after a system crash. For compatibility reasons, these +conditions are silently ignored if not satisfied. Currently, no way +is provided to test for them. +For more details, please reference mmap(2) man page: +http://man7.org/linux/man-pages/man2/mmap.2.html. 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 diff --git a/qemu-options.hx b/qemu-options.hx index 08749a3391..bdc74c0620 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4233,6 +4233,11 @@ 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 ensures the +file metadata is in sync for @option{mem-path} in case of host crash +or a power failure. MAP_SYNC requires support from both the host kernel +(since Linux kernel 4.15) and the filesystem of @option{mem-path} mounted +with DAX option. @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} -- 2.19.1 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=-8.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, 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 15CEFC10F14 for ; Mon, 22 Apr 2019 00:56:20 +0000 (UTC) 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.kernel.org (Postfix) with ESMTPS id D50A620833 for ; Mon, 22 Apr 2019 00:56:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D50A620833 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:58831 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hINFq-00007S-VM for qemu-devel@archiver.kernel.org; Sun, 21 Apr 2019 20:56:19 -0400 Received: from eggs.gnu.org ([209.51.188.92]:41617) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hINEd-0007lO-4o for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hINEc-0003dg-0U for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:03 -0400 Received: from mga18.intel.com ([134.134.136.126]:34181) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hINEb-0003cj-Og for qemu-devel@nongnu.org; Sun, 21 Apr 2019 20:55:01 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Apr 2019 17:55:00 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,379,1549958400"; d="scan'208";a="293416737" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga004.jf.intel.com with ESMTP; 21 Apr 2019 17:50:03 -0700 From: Wei Yang To: qemu-devel@nongnu.org Date: Mon, 22 Apr 2019 08:48:49 +0800 Message-Id: <20190422004849.26463-3-richardw.yang@linux.intel.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190422004849.26463-1-richardw.yang@linux.intel.com> References: <20190422004849.26463-1-richardw.yang@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.126 Subject: [Qemu-devel] [PATCH v14 2/2] 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: pagupta@redhat.com, xiaoguangrong.eric@gmail.com, mst@redhat.com, yi.z.zhang@linux.intel.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, stefanha@redhat.com, imammedo@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, ehabkost@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="UTF-8" Message-ID: <20190422004849.sIolv_GQJwqSk3Ra8l8pQfTq_35tDaTowSOhjq-XNbM@z> From: Zhang Yi Signed-off-by: Zhang Yi --- docs/nvdimm.txt | 22 +++++++++++++++++++--- qemu-options.hx | 5 +++++ 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 7231c2d78f..bcd1456e72 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -144,9 +144,25 @@ Guest Data Persistence ---------------------- Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one 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. +the only backend that can guarantee the guest write persistence is: + +A. DAX device (e.g., /dev/dax0.0, ) or +B. DAX file(mounted with dax option) + +When using B (A file supporting direct mapping of persistent memory) +as a backend, write persistence is guaranteed if the host kernel has +support for the MAP_SYNC flag in the mmap system call (available +since Linux 4.15 and on certain distro kernels) and additionally +both 'pmem' and 'share' flags are set to 'on' on the backend. + +If these conditions are not satisfied i.e. if either 'pmem' or 'share' +are not set, if the backend file does not support DAX or if MAP_SYNC +is not supported by the host kernel, write persistence is not +guaranteed after a system crash. For compatibility reasons, these +conditions are silently ignored if not satisfied. Currently, no way +is provided to test for them. +For more details, please reference mmap(2) man page: +http://man7.org/linux/man-pages/man2/mmap.2.html. 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 diff --git a/qemu-options.hx b/qemu-options.hx index 08749a3391..bdc74c0620 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4233,6 +4233,11 @@ 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 ensures the +file metadata is in sync for @option{mem-path} in case of host crash +or a power failure. MAP_SYNC requires support from both the host kernel +(since Linux kernel 4.15) and the filesystem of @option{mem-path} mounted +with DAX option. @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} -- 2.19.1