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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 76FD5C433E2 for ; Tue, 1 Sep 2020 17:13:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6247920767 for ; Tue, 1 Sep 2020 17:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732555AbgIARNb (ORCPT ); Tue, 1 Sep 2020 13:13:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:49588 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729519AbgIARNN (ORCPT ); Tue, 1 Sep 2020 13:13:13 -0400 Received: from gaia (unknown [46.69.195.127]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9625F2087D; Tue, 1 Sep 2020 17:13:09 +0000 (UTC) Date: Tue, 1 Sep 2020 18:13:07 +0100 From: Catalin Marinas To: chenzhou Cc: Dave Young , will@kernel.org, james.morse@arm.com, tglx@linutronix.de, mingo@redhat.com, bhe@redhat.com, corbet@lwn.net, John.P.donnelly@oracle.com, prabhakar.pkin@gmail.com, bhsharma@redhat.com, horms@verge.net.au, robh+dt@kernel.org, arnd@arndb.de, nsaenzjulienne@suse.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-doc@vger.kernel.org, guohanjun@huawei.com, xiexiuqi@huawei.com, huawei.libin@huawei.com, wangkefeng.wang@huawei.com Subject: Re: [PATCH v11 5/5] kdump: update Documentation about crashkernel Message-ID: <20200901171306.GK5561@gaia> References: <20200801130856.86625-1-chenzhou10@huawei.com> <20200801130856.86625-6-chenzhou10@huawei.com> <20200808100239.GB60590@dhcp-128-65.nay.redhat.com> <96d0da23-d484-7f66-1680-07b4b5984831@huawei.com> <20200810060355.GB6988@dhcp-128-65.nay.redhat.com> <2e6aebf9-3765-5d8c-933c-698442db1d52@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2e6aebf9-3765-5d8c-933c-698442db1d52@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 03:07:04PM +0800, chenzhou wrote: > On 2020/8/10 14:03, Dave Young wrote: > >>> Previously I remember we talked about to use similar logic as X86, but I > >>> remember you mentioned on some arm64 platform there could be no low > >>> memory at all. Is this not a problem now for the fallback? Just be > >>> curious, thanks for the update, for the common part looks good. > >> > >> Did you mean this discuss: https://lkml.org/lkml/2019/12/27/122? > > I meant about this reply instead :) > > https://lkml.org/lkml/2020/1/16/616 > > Sorry for not repley in time, I was on holiday last week. > > The platform James mentioned may exist for which have no devices and > need no low memory. If there is no memory below 4GB, the arm64 kernel assumes that the 32-bit devices will have some DMA offsets shifting the addresses to the bottom of the available RAM. So even if RAM starts above 4GB, we ZONE_DMA32 will be allocated in the bottom 4GB of the high memory (and if the hardware designers forgot to shift those DMA accesses, we don't have to support the platform ;)). So the arm64 notion of low memory differs slightly from the x86 one. -- Catalin