Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756553Ab3FLQyV (ORCPT ); Wed, 12 Jun 2013 12:54:21 -0400 Received: from out3-smtp.messagingengine.com ([66.111.4.27]:42221 "EHLO out3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754290Ab3FLQyU convert rfc822-to-8bit (ORCPT ); Wed, 12 Jun 2013 12:54:20 -0400 Message-Id: <1371056055.24587.140661243104889.29DDEEB4@webmail.messagingengine.com> X-Sasl-Enc: sPiSdnlq0CtLz61oUbrkzvzpF5whkLa4KYrGkl4SuPuu 1371056055 From: Simon Brown To: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: MessagingEngine.com Webmail Interface - ajax-5ae8e04c Subject: Accessing more than 2GB of memory with a 32 bit kernel Date: Wed, 12 Jun 2013 17:54:15 +0100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1671 Lines: 44 Hello, For the sake of an old prototype peripheral I'm using a non PAE 32 bit x86 kernel and I'm having trouble accessing memory above 2 GB. The system has 4GB installed and all is well with a PAE kernel. I'm obviously expecting to lose some memory due to memory mapped devices but I wasn't expecting to lose 2GB. Instead I'm suspecting a BIOS bug. The system reports: free -m total used free shared buffers cached Mem: 2012 491 1521 0 40 277 The mtrr table looked odd so I enabled sanitisation: [ 0.000000] original variable MTRRs [ 0.000000] reg 0, base: 2GB, range: 2GB, type UC [ 0.000000] reg 1, base: 0GB, range: 4GB, type WB [ 0.000000] reg 2, base: 4GB, range: 2GB, type WB [ 0.000000] total RAM covered: 4096M [ 0.000000] Found optimal setting for mtrr clean up [ 0.000000] gran_size: 64K chunk_size: 64K num_reg: 2 lose cover RAM: 0G [ 0.000000] New variable MTRRs [ 0.000000] reg 0, base: 0GB, range: 2GB, type WB [ 0.000000] reg 1, base: 4GB, range: 2GB, type WB I don't understand the gap in the new table. The motherboard is an Asus P5K with an Intel? P35 chipset. I'm using the ubuntu lucid kernel (2.6.32) but the problem is also present with the ubuntu precise kernel. I'm at the limit of my understanding, can anyone advise how to debug further? Thanks, Simon -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/