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=0.1 required=3.0 tests=DATE_IN_PAST_12_24, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 8C9B4C2BB1D for ; Thu, 12 Mar 2020 08:05:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B7DB206F1 for ; Thu, 12 Mar 2020 08:05:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726895AbgCLIFW (ORCPT ); Thu, 12 Mar 2020 04:05:22 -0400 Received: from mga03.intel.com ([134.134.136.65]:3476 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726254AbgCLIFV (ORCPT ); Thu, 12 Mar 2020 04:05:21 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Mar 2020 01:05:20 -0700 X-IronPort-AV: E=Sophos;i="5.70,544,1574150400"; d="scan'208";a="236744025" Received: from fpirou-mobl.ger.corp.intel.com (HELO localhost) ([10.252.52.195]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Mar 2020 01:05:18 -0700 From: "Patrick Ohly" To: Vivek Goyal , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, virtio-fs@redhat.com, miklos@szeredi.hu Cc: stefanha@redhat.com, dgilbert@redhat.com, mst@redhat.com Subject: Re: [PATCH 00/20] virtiofs: Add DAX support In-Reply-To: <20200304165845.3081-1-vgoyal@redhat.com> Organization: Intel GmbH, Dornacher Strasse 1, D-85622 Feldkirchen/Munich References: <20200304165845.3081-1-vgoyal@redhat.com> Date: Wed, 11 Mar 2020 14:38:03 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Vivek Goyal writes: > This patch series adds DAX support to virtiofs filesystem. This allows > bypassing guest page cache and allows mapping host page cache directly > in guest address space. > > When a page of file is needed, guest sends a request to map that page > (in host page cache) in qemu address space. Inside guest this is > a physical memory range controlled by virtiofs device. And guest > directly maps this physical address range using DAX and hence gets > access to file data on host. > > This can speed up things considerably in many situations. Also this > can result in substantial memory savings as file data does not have > to be copied in guest and it is directly accessed from host page > cache. As a potential user of this, let me make sure I understand the expected outcome: is the goal to let virtiofs use DAX (for increased performance, etc.) or also let applications that use virtiofs use DAX? You are mentioning using the host's page cache, so it's probably the former and MAP_SYNC on virtiofs will continue to be rejected, right? -- Best Regards Patrick Ohly