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 7F920C433E2 for ; Fri, 4 Sep 2020 06:39:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46EE720748 for ; Fri, 4 Sep 2020 06:39:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728389AbgIDGjh (ORCPT ); Fri, 4 Sep 2020 02:39:37 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:10812 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726251AbgIDGjh (ORCPT ); Fri, 4 Sep 2020 02:39:37 -0400 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id D6B3E21013686CF35EC2; Fri, 4 Sep 2020 14:39:33 +0800 (CST) Received: from [127.0.0.1] (10.174.176.220) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.487.0; Fri, 4 Sep 2020 14:39:23 +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> <20200904041633.GB11869@dhcp-128-65.nay.redhat.com> CC: Catalin Marinas , , , , , , , , , , , , , , , , , , , , , From: chenzhou Message-ID: <886c91a3-6729-e534-4d9d-b807c5584892@huawei.com> Date: Fri, 4 Sep 2020 14:39:21 +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: <20200904041633.GB11869@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-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 2020/9/4 12:16, Dave Young wrote: > On 09/04/20 at 12:02pm, chenzhou wrote: >> >> 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. > I feel starting with CRASH_ALIGN sounds better, can you just search from > CRASH_ALIGN in generic version? ok. > > Thanks > Dave > > > . >