From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754909Ab2ENI3Z (ORCPT ); Mon, 14 May 2012 04:29:25 -0400 Received: from plane.gmane.org ([80.91.229.3]:45331 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753479Ab2ENI3X (ORCPT ); Mon, 14 May 2012 04:29:23 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Cong Wang Subject: Re: [PATCH 0/2] kdump: Enter 2nd kernel with BSP for enabling multiple CPUs Date: Mon, 14 May 2012 08:29:08 +0000 (UTC) Message-ID: References: <20120416021951.9303.58568.stgit@localhost6.localdomain6> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: 203.114.244.89 User-Agent: slrn/0.9.9p1 (Linux) Cc: kexec@lists.infradead.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org So, the reason why you want to have multiple CPU's enabled in the 2nd kernel is to speed up the compression of the core dump? The first question is that, why the speed is important? Given the fact that the whole kdump progress happens automatically nowdays, there should be very few guys waiting for a kdump to complete, so the speed is not that important. Second, currently we use nr_cpus=1 for the 2nd kernel on RHEL6, to reduce the memory usage in the 2nd kernel. You mentioned 512M is a limit, but we want to make it even less, even 512M is not a good choice for us on x86. Bringing up more than 1 CPU will of course need more memory in the 2nd kernel. The limit is not only the size, but also the max address of loading initrd, which is 896M on x86 IIRC. A contiguos memory area larger than 512M usually sit above 869M, due to the fragmentation in the lower memory, so I am afraid you need to do (much?) more work. So, I am afraid you spend too much effort to fix a not-that-important issue, but I may miss something here... Thanks.