Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756174Ab0DFTxy (ORCPT ); Tue, 6 Apr 2010 15:53:54 -0400 Received: from terminus.zytor.com ([198.137.202.10]:35710 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753402Ab0DFTxt (ORCPT ); Tue, 6 Apr 2010 15:53:49 -0400 Message-ID: <4BBB8F07.60401@zytor.com> Date: Tue, 06 Apr 2010 12:44:07 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Frank Hu CC: Joel Fernandes , hayfeng Lee , linux-kernel@vger.kernel.org, linux-kernel@zh-kernel.org, kernelnewbies@nl.linux.org Subject: Re: why choose 896MB to the start point of ZONE_HIGHMEM References: <4BBB7AC9.5060008@zytor.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 803 Lines: 21 On 04/06/2010 12:20 PM, Frank Hu wrote: >> >> The ELF ABI specifies that user space has 3 GB available to it. That >> leaves 1 GB for the kernel. The kernel, by default, uses 128 MB for I/O >> mapping, vmalloc, and kmap support, which leaves 896 MB for LOWMEM. >> >> All of these boundaries are configurable; with PAE enabled the user >> space boundary has to be on a 1 GB boundary. >> > > the VM split is also configurable when building the kernel (for 32-bit > processors). I did say "all these boundaries are configurable". Rather explicitly. -hpa -- 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/