From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751525AbdJXF53 (ORCPT ); Tue, 24 Oct 2017 01:57:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50586 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750886AbdJXF52 (ORCPT ); Tue, 24 Oct 2017 01:57:28 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 0BB52356D0 Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=bhe@redhat.com Date: Tue, 24 Oct 2017 13:57:22 +0800 From: Baoquan He To: dyoung@redhat.com Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, vgoyal@redhat.com, yinghai@kernel.org, corbet@lwn.net Subject: Re: [PATCH 3/3] kdump: round up the total memory size to 128M for crashkernel reservation Message-ID: <20171024055722.GG27757@x1> References: <20171024053901.813846011@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171024053901.813846011@redhat.com> User-Agent: Mutt/1.7.0 (2016-08-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 24 Oct 2017 05:57:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dave, On 10/24/17 at 01:31pm, Dave Young wrote: > The total memory size we get in kernel is usually slightly less than 2G with a > 2G memory module machine. The main reason is bios/firmware reserve some area > it will not export all memory as usable to Linux. > > 2G memory X86 kvm guest test result of the total_mem value: > UEFI boot with ovmf: 0x7ef10000 > Legacy boot kvm guest: 0x7ff7cc00 > > An option is to use dmi/smbios to get physical memory size, but it's not > reliable as well. According to Prarit hardware vendors sometimes screw this up. > Thus we choose to round up total size to 128M to workaround this problem. > This is a best effort workaround, will improve it when we have better way > in the future. Thanks for this posting. While I don't get the point of this patch. So firmware take piece of memory, then why we need to count it into the total memory which we want to calculate a crashkernel memory based on. Not counting that, is there anyting incorrect? Thanks Baoquan > > Signed-off-by: Dave Young > --- > kernel/crash_core.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > --- linux.orig/kernel/crash_core.c > +++ linux/kernel/crash_core.c > @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem( > { > char *cur = cmdline, *tmp; > bool infinite_end = false; > + unsigned long long total_mem = system_ram; > + > + /* > + * Firmware usually reserves some memory regions for it's own use. > + * so we get less than actual system memory size. > + * We workaround this by round up the total size to 128M which is > + * enough for most test cases. > + */ > + total_mem = roundup(total_mem, 0x8000000); > > /* for each entry of the comma-separated list */ > do { > @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem( > return -EINVAL; > } > cur = tmp; > - if (size >= system_ram) { > + if (size >= total_mem) { > pr_warn("crashkernel: invalid size\n"); > return -EINVAL; > } > > /* match ? */ > - if (system_ram >= start && system_ram < end) { > + if (total_mem >= start && total_mem < end) { > *crash_size = size; > if (end == ULLONG_MAX) > infinite_end = true; > @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem( > pr_warn("Memory reservation scale order expected after '^'\n"); > return -EINVAL; > } > - size = (system_ram - *crash_size) >> shift; > + size = (total_mem - *crash_size) >> shift; > size = *crash_size + roundup(size, 1ULL << 20); > - if (size < system_ram) > + if (size < total_mem) > *crash_size = size; > cur = tmp; > } else > >