From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Sun, 31 Aug 2003 14:34:40 +0100 (BST) Received: from p508B6685.dip.t-dialin.net ([IPv6:::ffff:80.139.102.133]:38838 "EHLO dea.linux-mips.net") by linux-mips.org with ESMTP id ; Sun, 31 Aug 2003 14:34:38 +0100 Received: from dea.linux-mips.net (localhost [127.0.0.1]) by dea.linux-mips.net (8.12.8/8.12.8) with ESMTP id h7VDYa1p001916; Sun, 31 Aug 2003 15:34:37 +0200 Received: (from ralf@localhost) by dea.linux-mips.net (8.12.8/8.12.8/Submit) id h7VDYZDG001915; Sun, 31 Aug 2003 15:34:35 +0200 Date: Sun, 31 Aug 2003 15:34:34 +0200 From: Ralf Baechle To: Steve Madsen Cc: linux-mips@linux-mips.org Subject: Re: Using more than 256 MB of memory on SB1250 in 32-bit mode Message-ID: <20030831133434.GA23189@linux-mips.org> References: <3F4FCCD5.1000604@tadpole.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3F4FCCD5.1000604@tadpole.com> User-Agent: Mutt/1.4.1i Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 3113 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk X-list: linux-mips On Fri, Aug 29, 2003 at 02:59:49PM -0700, Steve Madsen wrote: > Is it possible to use more than 256 MB of system memory with the Broadcom > SB1250 in 32-bit mode? The memory map I'm looking at shows me that the > second 256 MB of memory is at physical address 0x80000000. I suspect that > due to the 2G/2G split in the kernel, I can't use memory this high without > moving to the 64-bit kernel. Steve Finney's answer was correct; I'd like to add a few details though. The explanation you gave isn't exactly right. A 2GB/2GB split would normally support 2GB of low memory. We don't on MIPS due to the very inconvenient and unchangable mappings of KSEG0/KSEG1 - something that may have been sweet in '85 when the address map was designed but not today when 32-bit address spaces are beginning to be fairly tight. Highmem works ok in 2.4 as long as you have a reasonably low ratio of highmem to lowmem. For typical loads that means going beyond 4:1 isn't sensible but the actual number may vary much based on exact system configuration or workload. Ralf