From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 20 Feb 2008 16:18:48 +0000 (GMT) Received: from localhost.localdomain ([127.0.0.1]:57571 "EHLO dl5rb.ham-radio-op.net") by ftp.linux-mips.org with ESMTP id S20030417AbYBTQSp (ORCPT ); Wed, 20 Feb 2008 16:18:45 +0000 Received: from denk.linux-mips.net (denk.linux-mips.net [127.0.0.1]) by dl5rb.ham-radio-op.net (8.14.1/8.13.8) with ESMTP id m1KGIjgY003684; Wed, 20 Feb 2008 16:18:45 GMT Received: (from ralf@localhost) by denk.linux-mips.net (8.14.1/8.14.1/Submit) id m1KGIirO003683; Wed, 20 Feb 2008 16:18:44 GMT Date: Wed, 20 Feb 2008 16:18:44 +0000 From: Ralf Baechle To: David VomLehn Cc: linux-mips@linux-mips.org Subject: Re: Does HIGHMEM work on 32-bit MIPS ports? Message-ID: <20080220161844.GC25644@linux-mips.org> References: <47BBA809.3050505@cisco.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47BBA809.3050505@cisco.com> User-Agent: Mutt/1.5.17 (2007-11-01) 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: 18279 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 Tue, Feb 19, 2008 at 08:09:45PM -0800, David VomLehn wrote: > As we continue to investigate using high memory on MIPS, we keep coming up > with odd results. The basic mapping of high memory seems to be working > correctly, and if we use an INITRAMFS root filesystem, things seem to work. > Things also seem to work with an NFS root filesystem if we disable > preemption, though we get someone squirrelly behavior in some minor ways. > Has anyone else successfully been able to use high memory on a 32-bit MIPS > Linux port? I've written MIPS highmem support in late 2002 for a customer who back then wasn't interested in being the first through the 64-bit minefield. Which back then certainly was justified - but there are now fairly stable 64-bit Linux kernels available so if you happen to be running on 64-bit hardware don't even spend a nanosecond on thinking about 32-bit highmem kernels. Highmem fundamentally sucks rocks through a straw. Coming back to your question. Highmem was only ever tested to work on SB1 and somewhat later PMC-Sierra RM9000 cores, both being 64-bit. With the increasing maturity of 64-bit Linux interest in these went away and as the result the highmem code started a slow bitrot - unnoticed for many moons. Ralf