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This document describes how to configure the Linux kernel to
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This document describes how to configure the Linux kernel to
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support more than 950MB physical RAM on x86 systems:
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support more than 950MB physical RAM on x86 systems:
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you only have to change the 'Max physical memory in MB' kernel
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you only have to change the 'Max physical memory in MB' kernel
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config option to get everything working. If you have less than
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config option to get everything working. If you have less than
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900M RAM, dont touch the default setting, this option buys you
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900M RAM, dont touch the default setting, this option buys you
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nothing at all! The option is in 'General setup':
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nothing at all! The option is in 'General setup':
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[ ] Kernel math emulation
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[ ] Kernel math emulation
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(1800) Max physical memory in MB
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(1800) Max physical memory in MB
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[*] Networking support
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[*] Networking support
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[ ] Limit memory to low 16MB
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[ ] Limit memory to low 16MB
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the unit of CONFIG_MAX_MEMSIZE is 'megabytes', ie. a value of
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the unit of CONFIG_MAX_MEMSIZE is 'megabytes', ie. a value of
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'1024' means '1024 MBytes'. Unless in 2.1 there is no restriction
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'1024' means '1024 MBytes'. Unless in 2.1 there is no restriction
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on the value of CONFIG_MAX_MEMSIZE!
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on the value of CONFIG_MAX_MEMSIZE!
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IMPORTANT: the value of CONFIG_MAX_MEMSIZE should be about 128M
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IMPORTANT: the value of CONFIG_MAX_MEMSIZE should be about 128M
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more than the amount of physical RAM (or 1024 if RAM is less than
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more than the amount of physical RAM (or 1024 if RAM is less than
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900M), because the kernel needs some space for it's own memory
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900M), because the kernel needs some space for it's own memory
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mappings. The kernel enforces this 128M window by clipping away
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mappings. The kernel enforces this 128M window by clipping away
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from the end of phsyical memory if necessary. (in this case that
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from the end of phsyical memory if necessary. (in this case that
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chunk of physical memory is not used by Linux!) So configure this
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chunk of physical memory is not used by Linux!) So configure this
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option carefully, and look at 'free' output and boot messages
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option carefully, and look at 'free' output and boot messages
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wether all RAM is correctly detected and configured.
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wether all RAM is correctly detected and configured.
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A system with 2G physical memory should use a value of ~2400, a
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A system with 2G physical memory should use a value of ~2400, a
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system with 3.8G memory should use something like 3900. A bit of
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system with 3.8G memory should use something like 3900. A bit of
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experimentation with the limit wont hurt, the kernel needs a ~128M
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experimentation with the limit wont hurt, the kernel needs a ~128M
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window for vmalloc() plus PCI space uses up some memory too, thus
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window for vmalloc() plus PCI space uses up some memory too, thus
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physical addresses above FD000000 should rather be kept free.
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physical addresses above FD000000 should rather be kept free.
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if the BIOS does not report correct memory size, use the mem= boot
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if the BIOS does not report correct memory size, use the mem= boot
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commandline option to override it.
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commandline option to override it.
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feel free to report any problems/suggestions to:
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feel free to report any problems/suggestions to:
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Ingo Molnar
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Ingo Molnar
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