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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 DF34BC33CA9 for ; Mon, 13 Jan 2020 19:44:09 +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 A98B121556 for ; Mon, 13 Jan 2020 19:44:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A98B121556 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nutanix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54994 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ir5dA-0008Fs-MS for qemu-devel@archiver.kernel.org; Mon, 13 Jan 2020 14:44:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41737) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ir5cK-0007AB-CE for qemu-devel@nongnu.org; Mon, 13 Jan 2020 14:43:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ir5cI-00077B-H6 for qemu-devel@nongnu.org; Mon, 13 Jan 2020 14:43:15 -0500 Received: from [192.146.154.1] (port=45159 helo=mcp01.nutanix.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ir5cI-00075u-8g for qemu-devel@nongnu.org; Mon, 13 Jan 2020 14:43:14 -0500 Received: from raphael-norwitz.user.nutanix.com (raphael-norwitz.dev.nutanix.com [10.41.25.241]) by mcp01.nutanix.com (Postfix) with ESMTP id 11725100693B; Mon, 13 Jan 2020 19:43:13 +0000 (UTC) Date: Mon, 13 Jan 2020 11:43:13 -0800 From: Raphael Norwitz To: mst@redhat.com, qemu-devel@nongnu.org Subject: Re: [RFC PATCH 0/3] vhost-user: Lift Max Ram Slots Limitation Message-ID: <20200113194313.GA73843@raphael-norwitz.user.nutanix.com> References: <1575874847-5792-1-git-send-email-raphael.norwitz@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1575874847-5792-1-git-send-email-raphael.norwitz@nutanix.com> User-Agent: Mutt/1.5.20 (2009-12-10) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 192.146.154.1 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Ping On Mon, Dec 09, 2019 at 02:00:44AM -0500, Raphael Norwitz wrote: >=20 > In QEMU today, a VM with a vhost-user device can hot add memory a > maximum of 8 times. See these threads, among others: >=20 > [1] https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg01046.html= =20 > https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg01236.html= =20 >=20 > [2] https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg04656.html= =20 >=20 > This RFC/patch set introduces a new protocol feature > VHOST_USER_PROTOCOL_F_CONFIGURE_SLOTS which, when enabled, lifts the > restriction on the maximum number RAM slots imposed by vhost-user. >=20 > The patch consists of 3 changes: > 1. Fixed Error Handling in vhost_user_set_mem_table_postcopy: > This is a bug fix in the postcopy migration path > 2. vhost-user: Refactor vhost_user_set_mem_table Functions: > This is a non-functional change refractoring the > vhost_user_set_mem_table and vhost_user_set_mem_table_postcopy > functions such that the feature can be more cleanly added. > 3. Introduce Configurable Number of Memory Slots Exposed by vhost-user: > This change introduces the new protocol feature > VHOST_USER_PROTOCOL_F_CONFIGURE_SLOTS. >=20 > The implementation details are explained in more detail in the commit > messages, but at a high level the new protocol feature works as follows= : > - If the VHOST_USER_PROTCOL_F_CONFIGURE_SLOTS feature is enabled, QEMU = will > send multiple VHOST_USER_ADD_MEM_REG and VHOST_USER_REM_MEM_REG > messages to map and unmap individual memory regions instead of one la= rge > VHOST_USER_SET_MEM_TABLE message containing all memory regions. > - The vhost-user struct maintains a =E2=80=99shadow state=E2=80=99 of m= emory regions > already sent to the guest. Each time vhost_user_set_mem_table is call= ed, > the shadow state is compared with the new device state. A > VHOST_USER_REM_MEM_REG will be sent for each region in the shadow sta= te > not in the device state. Then, a VHOST_USER_ADD_MEM_REG will be sent > for each region in the device state but not the shadow state. After > these messages have been sent, the shadow state will be updated to > reflect the new device state. >=20 > The VHOST_USER_SET_MEM_TABLE message was not reused because as the numb= er of > regions grows, the message becomes very large. In practice, such large > messages caused problems (truncated messages) and in the past it seems = the > community has opted for smaller fixed size messages where possible. VRI= NGs, > for example, are sent to the backend individually instead of in one mas= sive > message. >=20 > Current Limitations: > - postcopy migration is not supported when the > VHOST_USER_PROTOCOL_F_CONFIGURE_SLOTS has been negotiated.=20 > - VHOST_USER_PROTOCOL_F_CONFIGURE_SLOTS cannot be negotiated when > VHOST_USER_PROTOCOL_F_REPLY_ACK has also been negotiated. >=20 > Both of these limitations are due to resource contraints. They are not > imposed for technical reasons. >=20 > Questions: > - In the event transmitting a VHOST_USER_ADD_MEM_REG or > VHOST_USER_REM_REG message fails, is there any reason the error handl= ing > should differ from when transmitting VHOST_USER_SET_MEM_TABLE message= fails? > - Is there a cleaner way to ensure to ensure a postcopy migration canno= t be > started with this protocol feature enabled? >=20 > Best, > Raphael >=20 > Raphael Norwitz (3): > Fixed Error Handling in vhost_user_set_mem_table_postcopy > vhost-user: Refactor vhost_user_set_mem_table Functions > Introduce Configurable Number of Memory Slots Exposed by vhost-user: >=20 > docs/interop/vhost-user.rst | 43 +++++ > hw/virtio/vhost-user.c | 384 +++++++++++++++++++++++++++++++++---= -------- > 2 files changed, 335 insertions(+), 92 deletions(-) >=20 > --=20 > 1.8.3.1 >=20 >=20