Messages in this thread Patch in this message | | | Date | Mon, 18 May 1998 09:18:43 -0400 | From | Myrdraal <> | Subject | [PATCH] Revised Documentation/bigmem.txt |
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Hi, Thank you very much those who responded on my previous thread. Here is an updated version of Documentation/bigmem.txt. Better? -Myrdraal --- linux/Documentation/bigmem.txt.bak Sat May 16 22:48:06 1998 +++ linux/Documentation/bigmem.txt Mon May 18 09:18:37 1998 @@ -0,0 +1,47 @@ + x86 BIG MEMORY DOCUMENTATION v1.1 + ----------------------------------- + [Mon May 18 09:18:27 EDT 1998] + +* What is the purpose of this document? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The purpose of this document is to tell you how to set up Linux to work on +x86 machines with more then 950MB of RAM. If you do *not* have more then +950MB of RAM, you do not need to read any further. If you have an Alpha +or some other 64bit architecture, then you do not need to worry about this. + +* Okay, so what do I need to change? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +What you need to do is edit include/asm-i386/page.h and arch/i386/vmlinux.lds +and change where it has '0xC0000000' to some other value. Note that this +is in hexadecimal. + +* What does '0xC0000000' mean? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +0xC0000000 indicates that the kernel has a virtual address space of 1GB, +which means that the physical memory the kernel can use is limited to 950MB. + +* So, what am I supposed to change it to? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Well, for example, if you have 2GB of physical memory, you could change +it to 0x70000000. This would give your kernel slightly more then 2GB +of virtual memory. This is enough to map all your physical memory, plus +a bit more for various I/O memory mappings. + +* Why doesn't the kernel just default to letting you use 3gb physical memory? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Basically, it is a tradeoff between physical and virtual memory. The default +allows you to have 1gb physical memory (Slightly less, actually) and 3gb +virtual memory. 'virtual memory' means the size per process and the amount +of swap. If you set the maximum physical memory to 3gb, that means you only +have 1gb of virtual space (The x86 architecture is limited to 4gb physical +memory) - No one process could use more then 1gb of virtual memory. So you +would need multiple processes to use all your memory. mmap()ing files counts +as virtual memory. + +* I have more questions, who can I ask? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +You may feel free to send email to myrdraal@deathsdoor.com, and I will +respond as soon as possible. If that email address does not work, use +myrdraal@jackalz.dyn.ml.org. + -Myrdraal + | |