Date: Thu, 2 Aug 2001 09:38:00 -0400 (EDT) From: Kenneth Wayne Culver <culverk@wam.umd.edu> To: Rik van Riel <riel@conectiva.com.br> Cc: Terry Lambert <tlambert2@mindspring.com>, craig <craiglei@pasia.com.cn>, freebsd-hackers@FreeBSD.ORG Subject: Re: How to visit physical memory above 4G? Message-ID: <Pine.GSO.4.21.0108020937090.20844-100000@rac2.wam.umd.edu> In-Reply-To: <Pine.LNX.4.33L.0108020543070.5582-100000@duckman.distro.conectiva>
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Also, the PIII CAN'T natively support more than 4GB of ram. If a particular PIII motherboard supports this, then it's using some kind of wierd chipset that allows this to happen. 4GB is the limit with a 32 bit chip I believe; and the PIII is a 32-bit chip. Ken On Thu, 2 Aug 2001, Rik van Riel wrote: > On Wed, 1 Aug 2001, Terry Lambert wrote: > > > craig wrote: > > > > > > > > > I know PIII can support 64G physical memory. In FreeBSD how can I visit such > > > range memory(4G-64G) ? > > > > The short answer is "you can't". > > > > The longer answer is that you end up having to window it using > > segmentation; > > Only if you want to use it all within one process. > > You can have multiple 2 GB (that's the maximum > process size in FreeBSD, right?) programs at the > same time, happily using all physical memory. > > Only the FreeBSD memory management subsystem doesn't > support it (yet?). > > > This basically means that the memory is useless as a DMA target > > or source for disk controllers or gigabit ethernet cards, and is > > pretty useless for swap, ... > > > So for limited uses in data intensive applications, it might be > > usable, > > And for those data intensive applications, it is very > useful indeed... > > > But to directly answer your question: by rewriting much of the > > low core virtual memory and page mapping handling code to know > > about segmentation. > > Not just that. There is a more insidious problem with > the FreeBSD VM code and support of huge machines. > > The part of handling the PAE extended page table format > and mapping high memory pages in and out of KVA (kernel > virtual address) memory to copy stuff is easy. > > Problem is that you'll have to fit all of FreeBSD's VM > data structures in the 2GB of KVA. This just isn't going > to fit with the size the data structures have today ... > > So in order to support huge memory machines "right", > you'd have to put a number of FreeBSD's VM data structures > on a rather strict diet. > > regards, > > Rik > -- > Executive summary of a recent Microsoft press release: > "we are concerned about the GNU General Public License (GPL)" > > > http://www.surriel.com/ > http://www.conectiva.com/ http://distro.conectiva.com/ > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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