mm/swap.c

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 1 /*
 2  * linux/mm/swap.c
 3  *
 4  * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
 5  */
 6
 7 /*
 8  * This file contains the default values for the opereation of the
 9  * Linux VM subsystem. Finetuning documentation can be found in
 10  * linux/Documentation/sysctl/vm.txt.
 11  * Started 18.12.91
 12  * Swap aging added 23.2.95, Stephen Tweedie.
 13  * Buffermem limits added 12.3.98, Rik van Riel.
 14  */
 15
 16 #include <linux/mm.h>
 17 #include <linux/sched.h>
 18 #include <linux/head.h>
 19 #include <linux/kernel.h>
 20 #include <linux/kernel_stat.h>
 21 #include <linux/errno.h>
 22 #include <linux/string.h>
 23 #include <linux/stat.h>
 24 #include <linux/swap.h>
 25 #include <linux/fs.h>
 26 #include <linux/swapctl.h>
 27 #include <linux/pagemap.h>
 28 #include <linux/init.h>
 29
 30 #include <asm/dma.h>
 31 #include <asm/system.h>/* for cli()/sti() */
 32 #include <asm/uaccess.h>/* for copy_to/from_user */
 33 #include <asm/bitops.h>
 34 #include <asm/pgtable.h>
 35
 36 /*
 37  * We identify three levels of free memory. We never let free mem
 38  * fall below the freepages.min except for atomic allocations. We
 39  * start background swapping if we fall below freepages.high free
 40  * pages, and we begin intensive swapping below freepages.low.
 41  *
 42  * These values are there to keep GCC from complaining. Actual
 43  * initialization is done in mm/page_alloc.c or arch/sparc(64)/mm/init.c.
 44  */
 45 freepages_t freepages = {
 46 48,/* freepages.min */
 47 72,/* freepages.low */
 48 96/* freepages.high */
 49 };
 50
 51 /* We track the number of pages currently being asynchronously swapped
 52  out, so that we don't try to swap TOO many pages out at once */
 53 atomic_t nr_async_pages =ATOMIC_INIT(0);
 54
 55 /*
 56  * Constants for the page aging mechanism: the maximum age (actually,
 57  * the maximum "youthfulness"); the quanta by which pages rejuvenate
 58  * and age; and the initial age for new pages.
 59  */
 60
 61 swap_control_t swap_control = {
 62 20,3,1,3,/* Page aging */
 63 32,4,/* Aging cluster */
 64 8192,8192,/* Pageout and bufferout weights */
 65 };
 66
 67 swapstat_t swapstats = {0};
 68
 69 buffer_mem_t buffer_mem = {
 70 6,/* minimum percent buffer + cache memory */
 71 20,/* borrow percent buffer + cache memory */
 72 90/* maximum percent buffer + cache memory */
 73 };
 74