Documentation for /proc/sys/vm/* kernel version 2.2.10 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> For general info and legal blurb, please look in README. ============================================================== This file contains the documentation for the sysctl files in /proc/sys/vm and is valid for Linux kernel version 2.2. The files in this directory can be used to tune the operation of the virtual memory (VM) subsystem of the Linux kernel and the writeout of dirty data to disk. Default values and initialization routines for most of these files can be found in mm/swap.c. Currently, these files are in /proc/sys/vm: - overcommit_memory - page-cluster - dirty_ratio - dirty_background_ratio - dirty_expire_centisecs - dirty_writeback_centisecs - max_map_count - min_free_kbytes - laptop_mode - block_dump ============================================================== dirty_ratio, dirty_background_ratio, dirty_expire_centisecs, dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode, block_dump, swap_token_timeout: See Documentation/filesystems/proc.txt ============================================================== overcommit_memory: This value contains a flag that enables memory overcommitment. When this flag is 0, the kernel attempts to estimate the amount of free memory left when userspace requests more memory. When this flag is 1, the kernel pretends there is always enough memory until it actually runs out. When this flag is 2, the kernel uses a "never overcommit" policy that attempts to prevent any overcommit of memory. This feature can be very useful because there are a lot of programs that malloc() huge amounts of memory "just-in-case" and don't use much of it. The default value is 0. See Documentation/vm/overcommit-accounting and security/commoncap.c::cap_vm_enough_memory() for more information. ============================================================== overcommit_ratio: When overcommit_memory is set to 2, the committed address space is not permitted to exceed swap plus this percentage of physical RAM. See above. ============================================================== page-cluster: The Linux VM subsystem avoids excessive disk seeks by reading multiple pages on a page fault. The number of pages it reads is dependent on the amount of memory in your machine. The number of pages the kernel reads in at once is equal to 2 ^ page-cluster. Values above 2 ^ 5 don't make much sense for swap because we only cluster swap data in 32-page groups. ============================================================== max_map_count: This file contains the maximum number of memory map areas a process may have. Memory map areas are used as a side-effect of calling malloc, directly by mmap and mprotect, and also when loading shared libraries. While most applications need less than a thousand maps, certain programs, particularly malloc debuggers, may consume lots of them, e.g., up to one or two maps per allocation. The default value is 65536. ============================================================== min_free_kbytes: This is used to force the Linux VM to keep a minimum number of kilobytes free. The VM uses this number to compute a pages_min value for each lowmem zone in the system. Each lowmem zone gets a number of reserved free pages based proportionally on its size.