Date: Fri, 5 Jul 2002 06:35:15 -0700 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Daniel Lang <dl@leo.org> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Swap configuration for 2GB phys RAM Message-ID: <20020705133515.GA295@HAL9000.wox.org> In-Reply-To: <20020705113532.GA11273@atrbg11.informatik.tu-muenchen.de> References: <20020705113532.GA11273@atrbg11.informatik.tu-muenchen.de>
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Thus spake Daniel Lang <dl@leo.org>: > I've found in the handbook (could also be the FAQ) a paragraph > that stated, if the hardware (MMU) would support it, FreeBSD > could address 8 TB of (I guess virtual) memory. The poweredge > can even be equipped with 6 GB RAM, which is already past > the 4GB limit of a standard 32bit address space. So I wonder > if it would be possible to just use the memory as usual? No 32-bit architecture can address 8 TB of virtual memory with a flat address space. A single process can only address 2^32 bytes with 32-bit pointers. Furthermore, the kernel is mapped into every process' address space, reducing the room available. However, it is possible to have more than 4 GB of physical memory, and split it between several processes. On recent i386s, you can use up to 64 MB using bank switching, which is a bad idea that has been reinvented at least a dozen times. The comment that you read should probably say, ``If the hardware supported it a long time ago, someone would have revamped the FreeBSD VM to make use of the support by now.'' Nobody has bothered yet, to my knowledge, but rumor has it that Peter Wemm is working on it, and a few months ago I think David Greenman mentioned possibly doing the same. But a far better solution is to get a 64-bit processor. They can use more than 4 GB of physical memory The Right Way, and an individual virtual address space can be larger than 4 GB. Unfortunately, lots of third-party software doesn't work on 64-bit architectures. I've been struggling for a while to get a Java VM to work on ia64. That's because I need to run some Java programs that, like most Java programs, need to address more than 4 GB of RAM. Sigh. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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