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  */
  36 freepages_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? */
  43 int 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 */
  47 atomic_t nr_async_pages = ATOMIC_INIT(0);
  48
  49 buffer_mem_t buffer_mem = {
  50         2,      /* minimum percent buffer */
  51         10,     /* borrow percent buffer */
  52         60      /* maximum percent buffer */
  53 };
  54
  55 buffer_mem_t page_cache = {
  56         2,      /* minimum percent page cache */
  57         15,     /* borrow percent page cache */
  58         75      /* maximum */
  59 };
  60
  61 pager_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
  71 void __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 }