mm/swap.c

   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. Fine-tuning 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         96,     /* freepages.low */
  48         144     /* 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         5,      /* minimum percent buffer */
  71         25,     /* borrow percent buffer */
  72         50      /* maximum percent buffer */
  73 };
  74
  75 buffer_mem_t page_cache = {
  76         10,     /* minimum percent page cache */
  77         30,     /* borrow percent page cache */
  78         75      /* maximum */
  79 };
  80
  81 pager_daemon_t pager_daemon = {
  82         512,    /* base number for calculating the number of tries */
  83         SWAP_CLUSTER_MAX,       /* minimum number of tries */
  84         SWAP_CLUSTER_MAX,       /* do swap I/O in clusters of this size */
  85 };