From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 15 Oct 2003 16:00:03 +0100 (BST) Received: from p508B51CB.dip.t-dialin.net ([IPv6:::ffff:80.139.81.203]:63422 "EHLO dea.linux-mips.net") by linux-mips.org with ESMTP id ; Wed, 15 Oct 2003 15:59:51 +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 h9FExmNK030569; Wed, 15 Oct 2003 16:59:48 +0200 Received: (from ralf@localhost) by dea.linux-mips.net (8.12.8/8.12.8/Submit) id h9FExmLt030568; Wed, 15 Oct 2003 16:59:48 +0200 Date: Wed, 15 Oct 2003 16:59:48 +0200 From: Ralf Baechle To: "Maciej W. Rozycki" Cc: linux-mips@linux-mips.org Subject: MIPS addressing limits, Was: Re: CVS Update@-mips.org: linux Message-ID: <20031015145948.GB23514@linux-mips.org> References: <20031014132850.GA12938@linux-mips.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 3445 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 Wed, Oct 15, 2003 at 04:23:06PM +0200, Maciej W. Rozycki wrote: > > Still want more? A 3 level tree would then cover 128TB of virtual > > address space already exceedin the hardware limits of all processors but > > the R8000. > > Well, the MIPS64 ISA spec allows up to 8EB of user memory to be supported > by an implementation, IIRC; probably nothing supports that much yet, > though. ;-) BTW, is an R8000 spec available online anywhere? There used to be a few papers published by SGI online and various other bits of information I found through google. (I happen to have a paper copy of the R8000 manual but since the responsible people still haven't informed me if I can legally use it, this book is closed and will stay closed until this happens - if ever ... Pitty, I still receive mails from various R8000 users ...) > > 64k pagesize stretches the limits even further. Here a two level > > pagetable tree would cover 4TB, 3-level could cover 32PB exceeding > > the capacity of every MIPS processor ever made - and probably sufficient > > for the coming decade :-) > > Further increasing of the page size should result in better performance > due to fewer TLB misses and reduce the memory footprint of page tables, > but the drawback is more memory is wasted for maps. Whether the end > result is a gain or a loss depends on the actual application of a system, > so I guess we should either leave the size configurable (with a sane > default for those who might have troubles judging what would suit them > best) or only decide on a given size after lots of benchmarking. Unless somebody yells I almost feel like ditching 3-level pagetable support; 2-levels with a decent pagesize should suffice for a few years to come ... Ralf