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 E34FBC2D0C0 for ; Mon, 9 Dec 2019 09:39:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C089F20692 for ; Mon, 9 Dec 2019 09:39:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727576AbfLIJjG (ORCPT ); Mon, 9 Dec 2019 04:39:06 -0500 Received: from mx2.suse.de ([195.135.220.15]:43186 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727388AbfLIJjG (ORCPT ); Mon, 9 Dec 2019 04:39:06 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3F59BB1A3; Mon, 9 Dec 2019 09:39:04 +0000 (UTC) Subject: Re: [PATCH v3 0/1] xen/blkback: Squeeze page pools if a memory pressure To: SeongJae Park , axboe@kernel.dk, konrad.wilk@oracle.com, roger.pau@citrix.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, pdurrant@amazon.com, sj38.park@gmail.com, xen-devel@lists.xenproject.org References: <20191209085839.21215-1-sjpark@amazon.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <954f7beb-9d40-253e-260b-4750809bf808@suse.com> Date: Mon, 9 Dec 2019 10:39:02 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: <20191209085839.21215-1-sjpark@amazon.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09.12.19 09:58, SeongJae Park wrote: > Each `blkif` has a free pages pool for the grant mapping. The size of > the pool starts from zero and be increased on demand while processing > the I/O requests. If current I/O requests handling is finished or 100 > milliseconds has passed since last I/O requests handling, it checks and > shrinks the pool to not exceed the size limit, `max_buffer_pages`. > > Therefore, `blkfront` running guests can cause a memory pressure in the > `blkback` running guest by attaching a large number of block devices and > inducing I/O. I'm having problems to understand how a guest can attach a large number of block devices without those having been configured by the host admin before. If those devices have been configured, dom0 should be ready for that number of devices, e.g. by having enough spare memory area for ballooned pages. So either I'm missing something here or your reasoning for the need of the patch is wrong. Juergen