From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from oss.sgi.com (localhost [127.0.0.1]) by oss.sgi.com (8.12.3/8.12.3) with ESMTP id g4G3U2nC012304 for ; Wed, 15 May 2002 20:30:02 -0700 Received: (from majordomo@localhost) by oss.sgi.com (8.12.3/8.12.3/Submit) id g4G3U1B9012303 for linux-mips-outgoing; Wed, 15 May 2002 20:30:01 -0700 X-Authentication-Warning: oss.sgi.com: majordomo set sender to owner-linux-mips@oss.sgi.com using -f Received: from tibook.netx4.com (x1000-57.tellink.net [63.161.110.249]) by oss.sgi.com (8.12.3/8.12.3) with SMTP id g4G3TvnC012293 for ; Wed, 15 May 2002 20:29:57 -0700 Received: from embeddededge.com (IDENT:dan@localhost.localdomain [127.0.0.1]) by tibook.netx4.com (8.11.1/8.11.1) with ESMTP id g4G3SIP00680; Wed, 15 May 2002 23:28:22 -0400 Message-ID: <3CE32752.80109@embeddededge.com> Date: Wed, 15 May 2002 23:28:18 -0400 From: Dan Malek Organization: Embedded Edge, LLC. User-Agent: Mozilla/5.0 (X11; U; Linux ppc; en-US; rv:0.9.9) Gecko/20020411 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Jun Sun CC: Daniel Jacobowitz , Matthew Dharm , Linux-MIPS Subject: Re: MIPS 64? References: <20020515214818.GA1991@nevyn.them.org> <3CE2DA46.3070402@mvista.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mips@oss.sgi.com Precedence: bulk Jun Sun wrote: > So you really can't do 1.5GB on 32 bit kernel. > > It is interesting that PPC allows one to adjust user space size and > kernel space size. So on PPC you can get up to 2.5GB system RAM with > 1GB user space. Don't be confusing virtual/physical addressing. The highmem stuff allows access to larger physical address space by providing "windows" through the virtual space. The memory space configuration on PPC was done before highmem was working properly, but it has remained as an embedded configuration option. When using highmem, you obviously can't map all of the physical memory at once, so your applications and drivers have to coordinate what is mapped at a single instance. The PPC configuration option gives us a little flexibility to allow a little more kernel mapping for drivers when it is necessary (or to work around weird I/O mapping problems). Thanks. -- Dan