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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 45BDDC43381 for ; Mon, 25 Feb 2019 11:12:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1BA682087C for ; Mon, 25 Feb 2019 11:12:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726771AbfBYLM0 (ORCPT ); Mon, 25 Feb 2019 06:12:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40680 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726574AbfBYLM0 (ORCPT ); Mon, 25 Feb 2019 06:12:26 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F0BB53082E20; Mon, 25 Feb 2019 11:12:25 +0000 (UTC) Received: from dhcp-128-65.nay.redhat.com (ovpn-12-140.pek2.redhat.com [10.72.12.140]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 647535C21E; Mon, 25 Feb 2019 11:12:20 +0000 (UTC) Date: Mon, 25 Feb 2019 19:12:16 +0800 From: Dave Young To: Joerg Roedel Cc: Borislav Petkov , bhe@redhat.com, Jerry Hoemann , x86@kernel.org, Randy Dunlap , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Pingfan Liu , Mike Rapoport , Andrew Morton , yinghai@kernel.org, vgoyal@redhat.com, iommu@lists.linux-foundation.org, konrad.wilk@oracle.com Subject: Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr Message-ID: <20190225111216.GA9276@dhcp-128-65.nay.redhat.com> References: <20190211204816.GB21473@dhcp-128-65.nay.redhat.com> <20190215102458.GD10433@zn.tnic> <20190218014820.GA10711@dhcp-128-65.nay.redhat.com> <20190220083241.GA3447@zn.tnic> <20190220094146.GA8597@dhcp-128-65.nay.redhat.com> <20190221171321.GD12997@zn.tnic> <20190222021101.GA11654@dhcp-128-65.nay.redhat.com> <20190222084241.GC8380@suse.de> <20190222130026.GA30766@zn.tnic> <20190225110043.GA5884@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190225110043.GA5884@suse.de> User-Agent: Mutt/1.9.5 (2018-04-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Mon, 25 Feb 2019 11:12:26 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/25/19 at 12:00pm, Joerg Roedel wrote: > On Fri, Feb 22, 2019 at 02:00:26PM +0100, Borislav Petkov wrote: > > On Fri, Feb 22, 2019 at 09:42:41AM +0100, Joerg Roedel wrote: > > > The current default of 256MB was found by experiments on a bigger > > > number of machines, to create a reasonable default that is at least > > > likely to be sufficient of an average machine. > > > > Exactly, and this is what makes sense. > > > > The code should try the requested reservation and if it fails, it should > > try high allocation with default swiotlb size because we need to reserve > > *some* range. > > Right, makes sense. While at it, maybe it is time to move the default > allocation policy to 'high' again. The change was reverted six years ago > because it broke old kexec tools, but those are probably out-of-service > now. I think this change would make the whole crashdump allocation > process less fragile. One concern about this is for average cases, one do not need so much memory for kdump. For example in RHEL we use crashkernel=auto to automatically reserve kdump kernel memory, and for x86 the reserved size is like below now: 1G-64G:160M,64G-1T:256M,1T-:512M That means for a machine with less than 64G memory we only allocate 160M, it works for most machines in our lab. If we move to high as default, it will allocate 160M high + 256M low. It is too much for people who is good with the default 160M. Especially for virtual machine with less memory (but > 4G) To make the process less fragile maybe we can remove the 896M limitation and only try <4G then go to high. Thanks Dave