Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754993AbbG1JUE (ORCPT ); Tue, 28 Jul 2015 05:20:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60972 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752209AbbG1JUB (ORCPT ); Tue, 28 Jul 2015 05:20:01 -0400 Date: Tue, 28 Jul 2015 17:19:56 +0800 From: Baoquan He To: Yinghai Lu Cc: Dave Young , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , Andrew Morton , Jiri Kosina , Vivek Goyal , Linux Kernel Mailing List Subject: Re: [PATCH v2] Do not reserve crashkernel high memory if crashkernel low memory reserving failed Message-ID: <20150728091956.GC1720@dhcp-17-102.nay.redhat.com> References: <20150719145320.GB9968@dhcp-17-102.nay.redhat.com> <20150721073123.GA30649@dhcp-129-220.nay.redhat.com> <20150721075011.GC16747@dhcp-128-28.nay.redhat.com> <20150721082343.GC30649@dhcp-129-220.nay.redhat.com> <20150721085846.GA23020@dhcp-128-28.nay.redhat.com> <20150722005930.GE1834@dhcp-17-102.nay.redhat.com> <20150728005242.GB1720@dhcp-17-102.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2273 Lines: 45 On 07/27/15 at 07:45pm, Yinghai Lu wrote: > On Mon, Jul 27, 2015 at 5:52 PM, Baoquan He wrote: > > On 07/22/15 at 04:47pm, Yinghai Lu wrote: > > > > Sorry for late reply. This problem is reported by customers. They usulay > > don't like to make these things public. While for those systems with > > good hard iommu support, it could also fail to initialize hw iommu and > > then use swiotlb again, E.g in kdump kernel case. You can see in > > intel_iommu_init() swiotlb is assigned to 0 only if intel iommu (namely vt-d) > > is initialized successfully. There's possibility that hw iommu > > initialization will fail, in this case kdump kernel will fail to boot > > if no any low memory is given. So we can't make assumption that system > > can boot always well without low memory. > > When we had crashkernel=,high working with auto low=40M. > all system with crashkernel=,high worked. > Now come one model (assume it is 16 socket system), and it > could use crashkernel=,high crashkernel=256M,low. So it forces > all auto_low be 256M. Previously the default low memory was 64+8M (64M is for swiotlb). That value was changed since people complained their crash dumping failed because of insufficient low memory unexpectedly, almost 200M low memory is needed on their system when crashkernel=, high is specified. I think it makes sense to set a default low memory size to make systems work, specify a exact low memory size to make it better (for memory usage optimizing). > > That is ugly. If the customer does not want to make the log public to make > us to find good solution, why should we care about it ? > why not just let them carry the "crashkernel=256M,low" all the way? Now companies can provide big servers with tens of Tera bytes physical memory, I am not sure if this will leak information of their products. I will ask if a boot log is pasted here. They found the old default 72M low memory is not enough since they believe the old default low memory and then crash dump failed. > > Yinghai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/