From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757928Ab3APC27 (ORCPT ); Tue, 15 Jan 2013 21:28:59 -0500 Received: from terminus.zytor.com ([198.137.202.10]:46135 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756818Ab3APC26 (ORCPT ); Tue, 15 Jan 2013 21:28:58 -0500 Message-ID: <50F61061.4040201@zytor.com> Date: Tue, 15 Jan 2013 18:28:49 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: =?UTF-8?B?QWxleCBWaWxsYWPDrXMgTGFzc28=?= CC: linux-kernel@vger.kernel.org Subject: Re: Use of memmap= to forcibly recover memory in 3GB-4GB range - is this safe? References: <50F606A8.2080804@palosanto.com> In-Reply-To: <50F606A8.2080804@palosanto.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/15/2013 05:47 PM, Alex Villacís Lasso wrote: > > The system boots, apparently normally, and I can see the additional > "memory" in all system reports. However, I cannot quite shake the > feeling that this "memory" might be in fact an illusion, and an attempt > to use it will wrap around to the bottom of the memory and corrupt > anything there. Or worse. > > Some tests that I have tried: > 1) I have tried to occupy as much memory as possible, by starting two > virtual machines, plus one instance of eclipse, a browser, and a > bittorrent client, while running the graphical desktop. I have seen the > free memory (as reported by "top") fall to under 200 Mb with no apparent > instability, so this should prove that the extra memory is real, right? > 2) I have recompiled the kernel to support the memtest parameter. When > using it, the extra memory segment appears to be as healthy as other > areas of memory. However this might only mean that it is wrapping into > healthy low RAM. > > Is my reasoning sane? Is there a way to know, once and for all, whether > the extra "memory" is real and safe to use or not? Maybe you can get memtest86+ to test this phantom memory? But yes, it does sound like a BIOS bug. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.