From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753055AbbAZMLr (ORCPT ); Mon, 26 Jan 2015 07:11:47 -0500 Received: from 8bytes.org ([81.169.241.247]:46097 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751623AbbAZMLp (ORCPT ); Mon, 26 Jan 2015 07:11:45 -0500 Date: Mon, 26 Jan 2015 13:11:42 +0100 From: Joerg Roedel To: Borislav Petkov Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Konrad Rzeszutek Wilk , x86@kernel.org, linux-kernel@vger.kernel.org, Joerg Roedel Subject: Re: [PATCH 3/3] x86, crash: Allocate enough low-mem when crashkernel=high Message-ID: <20150126121142.GG30345@8bytes.org> References: <1420555874-11506-1-git-send-email-joro@8bytes.org> <1420555874-11506-4-git-send-email-joro@8bytes.org> <20150123170243.GG22635@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150123170243.GG22635@pd.tnic> 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 On Fri, Jan 23, 2015 at 06:02:43PM +0100, Borislav Petkov wrote: > On Tue, Jan 06, 2015 at 03:51:14PM +0100, Joerg Roedel wrote: > > From: Joerg Roedel > > > > When the crashkernel is loaded above 4GiB in memory the > > first kernel only allocates 72MiB of low-memory for the DMA > > requirements of the second kernel. On systems with many > > devices this is not enough and causes device driver > > initialization errors and failed crash dumps. Set this > > default value to 256MiB to make sure there is enough memory > > This upper limit of 256 looks arbitrary. Are we going to raise it a > couple of years from now if it becomes insufficient then? Yes, it is arbitrary. I am open for suggestions on what might be a proper value to satisfy most systems. > It probably won't be easy but is there some more reliable way to > allocate enough memory for DMA on a say per-system basis or whatever...? > Probably not but let me ask it anyway. Well, there is no easy way. But we could collect information from the loaded drivers on boot about how many dma-memory they allocate and base our allocation on that. Or we solve it in user-space by some more cleverness in creating the kernel command-line for crashkernel=high. But besides that, I think the first two patches of this set make sense anyway. I understand that the third one is debatable. Joerg