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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. | ||