Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755234AbbG1Aws (ORCPT ); Mon, 27 Jul 2015 20:52:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38472 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754960AbbG1Awr (ORCPT ); Mon, 27 Jul 2015 20:52:47 -0400 Date: Tue, 28 Jul 2015 08:52:42 +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: <20150728005242.GB1720@dhcp-17-102.nay.redhat.com> References: <1437304064-9916-1-git-send-email-bhe@redhat.com> <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> 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: 1336 Lines: 28 On 07/22/15 at 04:47pm, Yinghai Lu wrote: > On Tue, Jul 21, 2015 at 5:59 PM, Baoquan He wrote: > >> That commit should only be used to workaround some systems that > >> have partial iommu support. > > > > Those big servers mostly has hardware iommu. But they still can > > enable swiotlb suport. Then low memory is needed. > > Do you have whole bootlog? I don't understand why those system can not use > full iommu. BIOS problem or HW/silicon limitation? 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. Thanks Baoquan -- 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/