| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | There are several classic problems related to memory on Linux |
| 2 | systems. |
| 3 | |
| 4 | 1) There are some buggy motherboards which cannot properly |
| 5 | deal with the memory above 16MB. Consider exchanging |
| 6 | your motherboard. |
| 7 | |
| 8 | 2) You cannot do DMA on the ISA bus to addresses above |
| 9 | 16M. Most device drivers under Linux allow the use |
| 10 | of bounce buffers which work around this problem. Drivers |
| 11 | that don't use bounce buffers will be unstable with |
| 12 | more than 16M installed. Drivers that use bounce buffers |
| 13 | will be OK, but may have slightly higher overhead. |
| 14 | |
| 15 | 3) There are some motherboards that will not cache above |
| 16 | a certain quantity of memory. If you have one of these |
| 17 | motherboards, your system will be SLOWER, not faster |
| 18 | as you add more memory. Consider exchanging your |
| 19 | motherboard. |
| 20 | |
| 21 | All of these problems can be addressed with the "mem=XXXM" boot option |
| 22 | (where XXX is the size of RAM to use in megabytes). |
| 23 | It can also tell Linux to use less memory than is actually installed. |
| 24 | If you use "mem=" on a machine with PCI, consider using "memmap=" to avoid |
| 25 | physical address space collisions. |
| 26 | |
| 27 | See the documentation of your boot loader (LILO, loadlin, etc.) about |
| 28 | how to pass options to the kernel. |
| 29 | |
| 30 | There are other memory problems which Linux cannot deal with. Random |
| 31 | corruption of memory is usually a sign of serious hardware trouble. |
| 32 | Try: |
| 33 | |
| 34 | * Reducing memory settings in the BIOS to the most conservative |
| 35 | timings. |
| 36 | |
| 37 | * Adding a cooling fan. |
| 38 | |
| 39 | * Not overclocking your CPU. |
| 40 | |
| 41 | * Having the memory tested in a memory tester or exchanged |
| 42 | with the vendor. Consider testing it with memtest86 yourself. |
| 43 | |
| 44 | * Exchanging your CPU, cache, or motherboard for one that works. |
| 45 | |
| 46 | * Disabling the cache from the BIOS. |
| 47 | |
| 48 | * Try passing the "mem=4M" option to the kernel to limit |
| 49 | Linux to using a very small amount of memory. Use "memmap="-option |
| 50 | together with "mem=" on systems with PCI to avoid physical address |
| 51 | space collisions. |
| 52 | |
| 53 | |
| 54 | Other tricks: |
| 55 | |
| 56 | * Try passing the "no-387" option to the kernel to ignore |
| 57 | a buggy FPU. |
| 58 | |
| 59 | * Try passing the "no-hlt" option to disable the potentially |
| 60 | buggy HLT instruction in your CPU. |