Date: Thu, 02 Aug 2001 09:33:40 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: Terry Lambert <tlambert2@mindspring.com> Cc: freebsd-hackers@FreeBSD.org, craig <craiglei@pasia.com.cn> Subject: Re: How to visit physical memory above 4G? Message-ID: <XFMail.010802093340.jhb@FreeBSD.org> In-Reply-To: <3B68F190.AB04ACB3@mindspring.com>
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On 02-Aug-01 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; if you are familiar with the 4k window on video > memory in the TI 99/4A, or the bank select on the 6510 (e.g. > the ability to select between 32K of RAM, and 32K of ROM, but > not both at the same time, on the Commodore C-64 and the similar > arrangement on the C-128, etc.), then you;ll have an idea of how > the thing works... assuming you can find a motherboard that can > handle it. Err. hang on. This has zero to do with segmentation. Zip, nada. PAE is completely in the paging side of things. No matter what fun games you play with segmentation, you still end up with a 32-bit linear address that gets handed off to the paging translations. PAE just allows you to use more backing store across multiple processes, but you are still stuck with a 4gb virtual address space for processes. (Including KVM) > But to directly answer your question: by rewriting much of the > low core virtual memory and page mapping handling code to know > about segmentation. No, to rewrite said code to handle a different type of page table structure. -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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