Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame^] | 1 | Documentation for /proc/sys/vm/* kernel version 2.2.10 |
| 2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> |
| 3 | |
| 4 | For general info and legal blurb, please look in README. |
| 5 | |
| 6 | ============================================================== |
| 7 | |
| 8 | This file contains the documentation for the sysctl files in |
| 9 | /proc/sys/vm and is valid for Linux kernel version 2.2. |
| 10 | |
| 11 | The files in this directory can be used to tune the operation |
| 12 | of the virtual memory (VM) subsystem of the Linux kernel and |
| 13 | the writeout of dirty data to disk. |
| 14 | |
| 15 | Default values and initialization routines for most of these |
| 16 | files can be found in mm/swap.c. |
| 17 | |
| 18 | Currently, these files are in /proc/sys/vm: |
| 19 | - overcommit_memory |
| 20 | - page-cluster |
| 21 | - dirty_ratio |
| 22 | - dirty_background_ratio |
| 23 | - dirty_expire_centisecs |
| 24 | - dirty_writeback_centisecs |
| 25 | - max_map_count |
| 26 | - min_free_kbytes |
| 27 | - laptop_mode |
| 28 | - block_dump |
| 29 | |
| 30 | ============================================================== |
| 31 | |
| 32 | dirty_ratio, dirty_background_ratio, dirty_expire_centisecs, |
| 33 | dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode, |
| 34 | block_dump, swap_token_timeout: |
| 35 | |
| 36 | See Documentation/filesystems/proc.txt |
| 37 | |
| 38 | ============================================================== |
| 39 | |
| 40 | overcommit_memory: |
| 41 | |
| 42 | This value contains a flag that enables memory overcommitment. |
| 43 | |
| 44 | When this flag is 0, the kernel attempts to estimate the amount |
| 45 | of free memory left when userspace requests more memory. |
| 46 | |
| 47 | When this flag is 1, the kernel pretends there is always enough |
| 48 | memory until it actually runs out. |
| 49 | |
| 50 | When this flag is 2, the kernel uses a "never overcommit" |
| 51 | policy that attempts to prevent any overcommit of memory. |
| 52 | |
| 53 | This feature can be very useful because there are a lot of |
| 54 | programs that malloc() huge amounts of memory "just-in-case" |
| 55 | and don't use much of it. |
| 56 | |
| 57 | The default value is 0. |
| 58 | |
| 59 | See Documentation/vm/overcommit-accounting and |
| 60 | security/commoncap.c::cap_vm_enough_memory() for more information. |
| 61 | |
| 62 | ============================================================== |
| 63 | |
| 64 | overcommit_ratio: |
| 65 | |
| 66 | When overcommit_memory is set to 2, the committed address |
| 67 | space is not permitted to exceed swap plus this percentage |
| 68 | of physical RAM. See above. |
| 69 | |
| 70 | ============================================================== |
| 71 | |
| 72 | page-cluster: |
| 73 | |
| 74 | The Linux VM subsystem avoids excessive disk seeks by reading |
| 75 | multiple pages on a page fault. The number of pages it reads |
| 76 | is dependent on the amount of memory in your machine. |
| 77 | |
| 78 | The number of pages the kernel reads in at once is equal to |
| 79 | 2 ^ page-cluster. Values above 2 ^ 5 don't make much sense |
| 80 | for swap because we only cluster swap data in 32-page groups. |
| 81 | |
| 82 | ============================================================== |
| 83 | |
| 84 | max_map_count: |
| 85 | |
| 86 | This file contains the maximum number of memory map areas a process |
| 87 | may have. Memory map areas are used as a side-effect of calling |
| 88 | malloc, directly by mmap and mprotect, and also when loading shared |
| 89 | libraries. |
| 90 | |
| 91 | While most applications need less than a thousand maps, certain |
| 92 | programs, particularly malloc debuggers, may consume lots of them, |
| 93 | e.g., up to one or two maps per allocation. |
| 94 | |
| 95 | The default value is 65536. |
| 96 | |
| 97 | ============================================================== |
| 98 | |
| 99 | min_free_kbytes: |
| 100 | |
| 101 | This is used to force the Linux VM to keep a minimum number |
| 102 | of kilobytes free. The VM uses this number to compute a pages_min |
| 103 | value for each lowmem zone in the system. Each lowmem zone gets |
| 104 | a number of reserved free pages based proportionally on its size. |