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=-7.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 01AEDC433E2 for ; Fri, 4 Sep 2020 04:04:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF362206CA for ; Fri, 4 Sep 2020 04:04:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726308AbgIDEEw (ORCPT ); Fri, 4 Sep 2020 00:04:52 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:10810 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725765AbgIDEEv (ORCPT ); Fri, 4 Sep 2020 00:04:51 -0400 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 0B4F9C60C5D1EFC19866; Fri, 4 Sep 2020 12:02:13 +0800 (CST) Received: from [127.0.0.1] (10.174.176.220) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.487.0; Fri, 4 Sep 2020 12:02:06 +0800 Subject: Re: [PATCH v11 3/5] arm64: kdump: reimplement crashkernel=X To: Dave Young References: <20200801130856.86625-1-chenzhou10@huawei.com> <20200801130856.86625-4-chenzhou10@huawei.com> <20200902170910.GB16673@gaia> <20200904030424.GA11384@dhcp-128-65.nay.redhat.com> <20200904031014.GA11869@dhcp-128-65.nay.redhat.com> CC: Catalin Marinas , , , , , , , , , , , , , , , , , , , , , From: chenzhou Message-ID: Date: Fri, 4 Sep 2020 12:02:05 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20200904031014.GA11869@dhcp-128-65.nay.redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.176.220] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/9/4 11:10, Dave Young wrote: > On 09/04/20 at 11:04am, Dave Young wrote: >> On 09/03/20 at 07:26pm, chenzhou wrote: >>> Hi Catalin, >>> >>> >>> On 2020/9/3 1:09, Catalin Marinas wrote: >>>> On Sat, Aug 01, 2020 at 09:08:54PM +0800, Chen Zhou wrote: >>>>> There are following issues in arm64 kdump: >>>>> 1. We use crashkernel=X to reserve crashkernel below 4G, which >>>>> will fail when there is no enough low memory. >>>>> 2. If reserving crashkernel above 4G, in this case, crash dump >>>>> kernel will boot failure because there is no low memory available >>>>> for allocation. >>>>> 3. Since commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32"), >>>>> if the memory reserved for crash dump kernel falled in ZONE_DMA32, >>>>> the devices in crash dump kernel need to use ZONE_DMA will alloc >>>>> fail. >>>>> >>>>> To solve these issues, change the behavior of crashkernel=X. >>>>> crashkernel=X tries low allocation in ZONE_DMA, and fall back to >>>>> high allocation if it fails. >>>>> >>>>> If requized size X is too large and leads to very little free memory >>>>> in ZONE_DMA after low allocation, the system may not work normally. >>>>> So add a threshold and go for high allocation directly if the required >>>>> size is too large. The value of threshold is set as the half of >>>>> the low memory. >>>>> >>>>> If crash_base is outside ZONE_DMA, try to allocate at least 256M in >>>>> ZONE_DMA automatically. "crashkernel=Y,low" can be used to allocate >>>>> specified size low memory. >>>> Except for the threshold to keep zone ZONE_DMA memory, >>>> reserve_crashkernel() looks very close to the x86 version. Shall we try >>>> to make this generic as well? In the first instance, you could avoid the >>>> threshold check if it takes an explicit ",high" option. >>> Ok, i will try to do this. >>> >>> I look into the function reserve_crashkernel() of x86 and found the start address is >>> CRASH_ALIGN in function memblock_find_in_range(), which is different with arm64. >>> >>> I don't figure out why is CRASH_ALIGN in x86, is there any specific reason? >> Hmm, took another look at the option CONFIG_PHYSICAL_ALIGN >> config PHYSICAL_ALIGN >> hex "Alignment value to which kernel should be aligned" >> default "0x200000" >> range 0x2000 0x1000000 if X86_32 >> range 0x200000 0x1000000 if X86_64 >> >> According to above, I think the 16M should come from the largest value >> But the default value is 2M, with smaller value reservation can have >> more chance to succeed. >> >> It seems we still need arch specific CRASH_ALIGN, but the initial >> version you added the #ifdef for different arches, can you move the >> macro to arch specific headers? > And just keep the x86 align value as is, I can try to change the x86 > value later to CONFIG_PHYSICAL_ALIGN, in this way this series can be > cleaner. Ok. I have no question about the value of macro CRASH_ALIGN, instead the lower bound of memblock_find_in_range(). For x86, in reserve_crashkernel()，restrict the lower bound of the range to CRASH_ALIGN, ... crash_base = memblock_find_in_range(CRASH_ALIGN, CRASH_ADDR_LOW_MAX, crash_size, CRASH_ALIGN); ... in reserve_crashkernel_low()，with no this restriction. ... low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN); ... How about all making memblock_find_in_range() search from the start of memory? If it is ok, i will do like this in the generic version. Thanks, Chen Zhou > >> Thanks >> Dave > > . >