LXR linux-old/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/kernel_stat.h>
  18#include <linux/swap.h>
  19#include <linux/swapctl.h>
  20#include <linux/pagemap.h>
  21#include <linux/init.h>
  22
  23#include <asm/dma.h>
  24#include <asm/uaccess.h> /* for copy_to/from_user */
  25#include <asm/pgtable.h>
  26
  27/*
  28 * We identify three levels of free memory.  We never let free mem
  29 * fall below the freepages.min except for atomic allocations.  We
  30 * start background swapping if we fall below freepages.high free
  31 * pages, and we begin intensive swapping below freepages.low.
  32 *
  33 * These values are there to keep GCC from complaining. Actual
  34 * initialization is done in mm/page_alloc.c or arch/sparc(64)/mm/init.c.
  35 */
  36freepages_t freepages = {
  37        48,     /* freepages.min */
  38        96,     /* freepages.low */
  39        144     /* freepages.high */
  40};
  41
  42/* How many pages do we try to swap or page in/out together? */
  43int page_cluster = 4; /* Default value modified in swap_setup() */
  44
  45/* We track the number of pages currently being asynchronously swapped
  46   out, so that we don't try to swap TOO many pages out at once */
  47atomic_t nr_async_pages = ATOMIC_INIT(0);
  48
  49buffer_mem_t buffer_mem = {
  50        2,      /* minimum percent buffer */
  51        10,     /* borrow percent buffer */
  52        60      /* maximum percent buffer */
  53};
  54
  55buffer_mem_t page_cache = {
  56        2,      /* minimum percent page cache */
  57        15,     /* borrow percent page cache */
  58        75      /* maximum */
  59};
  60
  61pager_daemon_t pager_daemon = {
  62        512,    /* base number for calculating the number of tries */
  63        SWAP_CLUSTER_MAX,       /* minimum number of tries */
  64        SWAP_CLUSTER_MAX,       /* do swap I/O in clusters of this size */
  65};
  66
  67/*
  68 * Perform any setup for the swap system
  69 */
  70
  71void __init swap_setup(void)
  72{
  73        /* Use a smaller cluster for memory <16MB or <32MB */
  74        if (num_physpages < ((16 * 1024 * 1024) >> PAGE_SHIFT))
  75                page_cluster = 2;
  76        else if (num_physpages < ((32 * 1024 * 1024) >> PAGE_SHIFT))
  77                page_cluster = 3;
  78        else
  79                page_cluster = 4;
  80}
  81