mm/swap.c

37397 /*
37398  *  linux/mm/swap.c
37399  *
37400  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
37401  */
37402 
37403 /* This file contains the default values for the
37404  * opereation of the Linux VM subsystem. Fine-tuning
37405  * documentation can be found in
37406  * linux/Documentation/sysctl/vm.txt.
37407  * Started 18.12.91
37408  * Swap aging added 23.2.95, Stephen Tweedie.
37409  * Buffermem limits added 12.3.98, Rik van Riel.
37410  */
37411 
37412 #include <linux/mm.h>
37413 #include <linux/kernel_stat.h>
37414 #include <linux/swap.h>
37415 #include <linux/swapctl.h>
37416 #include <linux/pagemap.h>
37417 #include <linux/init.h>
37418 
37419 #include <asm/dma.h>
37420 #include <asm/uaccess.h> /* for copy_to/from_user */
37421 #include <asm/pgtable.h>
37422 
37423 /* We identify three levels of free memory.  We never let
37424  * free mem fall below the freepages.min except for
37425  * atomic allocations.  We start background swapping if
37426  * we fall below freepages.high free pages, and we begin
37427  * intensive swapping below freepages.low.
37428  *
37429  * These values are there to keep GCC from
37430  * complaining. Actual initialization is done in
37431  * mm/page_alloc.c or arch/sparc(64)/mm/init.c.  */
37432 freepages_t freepages = {
37433   48,     /* freepages.min */
37434   96,     /* freepages.low */
37435   144     /* freepages.high */
37436 };
37437 
37438 /* How many pages do we try to swap or page in/out
37439  * together? */
37440 /* Default modified in swap_setup() */
37441 int page_cluster = 4;
37442 
37443 /* We track the number of pages currently being
37444  * asynchronously swapped out, so that we don't try to
37445  * swap TOO many pages out at once */
37446 atomic_t nr_async_pages = ATOMIC_INIT(0);
37447 
37448 buffer_mem_t buffer_mem = {
37449   2,      /* minimum percent buffer */
37450   10,     /* borrow percent buffer */
37451   60      /* maximum percent buffer */
37452 };
37453 
37454 buffer_mem_t page_cache = {
37455   2,      /* minimum percent page cache */
37456   15,     /* borrow percent page cache */
37457   75      /* maximum */
37458 };
37459 
37460 pager_daemon_t pager_daemon = {
37461   512,  /* base # for calculating the number of tries */
37462   SWAP_CLUSTER_MAX, /* minimum number of tries */
37463   SWAP_CLUSTER_MAX, /* swap I/O in clusters of this sz */
37464 };
37465 
37466 /* Perform any setup for the swap system */
37467 
37468 void __init swap_setup(void)
37469 {
37470   /* Use a smaller cluster for memory <16MB or <32MB */
37471   if (num_physpages < ((16 * 1024 * 1024) >> PAGE_SHIFT))
37472     page_cluster = 2;
37473   else if (num_physpages <
37474            ((32 * 1024 * 1024) >> PAGE_SHIFT))
37475     page_cluster = 3;
37476   else
37477     page_cluster = 4;
37478 }