swap.c

LINUX1.0源代码,代码条理清晰

/*
 *  linux/mm/swap.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * This file should contain most things doing the swapping from/to disk.
 * Started 18.12.91
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/stat.h>

#include <asm/system.h> /* for cli()/sti() */
#include <asm/bitops.h>

#define MAX_SWAPFILES 8

#define SWP_USED	1
#define SWP_WRITEOK	3

#define SWP_TYPE(entry) (((entry) & 0xfe) >> 1)
#define SWP_OFFSET(entry) ((entry) >> PAGE_SHIFT)
#define SWP_ENTRY(type,offset) (((type) << 1) | ((offset) << PAGE_SHIFT))

static int nr_swapfiles = 0;
static struct wait_queue * lock_queue = NULL;

static struct swap_info_struct {
	unsigned long flags;
	struct inode * swap_file;
	unsigned int swap_device;
	unsigned char * swap_map;
	unsigned char * swap_lockmap;
	int pages;
	int lowest_bit;
	int highest_bit;
	unsigned long max;
} swap_info[MAX_SWAPFILES];

extern unsigned long free_page_list;
extern int shm_swap (int);

/*
 * The following are used to make sure we don't thrash too much...
 * NOTE!! NR_LAST_FREE_PAGES must be a power of 2...
 */
#define NR_LAST_FREE_PAGES 32
static unsigned long last_free_pages[NR_LAST_FREE_PAGES] = {0,};

void rw_swap_page(int rw, unsigned long entry, char * buf)
{
	unsigned long type, offset;
	struct swap_info_struct * p;

	type = SWP_TYPE(entry);
	if (type >= nr_swapfiles) {
		printk("Internal error: bad swap-device\n");
		return;
	}
	p = &swap_info[type];
	offset = SWP_OFFSET(entry);
	if (offset >= p->max) {
		printk("rw_swap_page: weirdness\n");
		return;
	}
	if (!(p->flags & SWP_USED)) {
		printk("Trying to swap to unused swap-device\n");
		return;
	}
	while (set_bit(offset,p->swap_lockmap))
		sleep_on(&lock_queue);
	if (rw == READ)
		kstat.pswpin++;
	else
		kstat.pswpout++;
	if (p->swap_device) {
		ll_rw_page(rw,p->swap_device,offset,buf);
	} else if (p->swap_file) {
		unsigned int zones[8];
		unsigned int block;
		int i, j;

		block = offset << (12 - p->swap_file->i_sb->s_blocksize_bits);

		for (i=0, j=0; j< PAGE_SIZE ; i++, j +=p->swap_file->i_sb->s_blocksize)
			if (!(zones[i] = bmap(p->swap_file,block++))) {
				printk("rw_swap_page: bad swap file\n");
				return;
			}
		ll_rw_swap_file(rw,p->swap_file->i_dev, zones, i,buf);
	} else
		printk("re_swap_page: no swap file or device\n");
	if (offset && !clear_bit(offset,p->swap_lockmap))
		printk("rw_swap_page: lock already cleared\n");
	wake_up(&lock_queue);
}

unsigned int get_swap_page(void)
{
	struct swap_info_struct * p;
	unsigned int offset, type;

	p = swap_info;
	for (type = 0 ; type < nr_swapfiles ; type++,p++) {
		if ((p->flags & SWP_WRITEOK) != SWP_WRITEOK)
			continue;
		for (offset = p->lowest_bit; offset <= p->highest_bit ; offset++) {
			if (p->swap_map[offset])
				continue;
			p->swap_map[offset] = 1;
			nr_swap_pages--;
			if (offset == p->highest_bit)
				p->highest_bit--;
			p->lowest_bit = offset;
			return SWP_ENTRY(type,offset);
		}
	}
	return 0;
}

unsigned long swap_duplicate(unsigned long entry)
{
	struct swap_info_struct * p;
	unsigned long offset, type;

	if (!entry)
		return 0;
	offset = SWP_OFFSET(entry);
	type = SWP_TYPE(entry);
	if (type == SHM_SWP_TYPE)
		return entry;
	if (type >= nr_swapfiles) {
		printk("Trying to duplicate nonexistent swap-page\n");
		return 0;
	}
	p = type + swap_info;
	if (offset >= p->max) {
		printk("swap_free: weirdness\n");
		return 0;
	}
	if (!p->swap_map[offset]) {
		printk("swap_duplicate: trying to duplicate unused page\n");
		return 0;
	}
	p->swap_map[offset]++;
	return entry;
}

void swap_free(unsigned long entry)
{
	struct swap_info_struct * p;
	unsigned long offset, type;

	if (!entry)
		return;
	type = SWP_TYPE(entry);
	if (type == SHM_SWP_TYPE)
		return;
	if (type >= nr_swapfiles) {
		printk("Trying to free nonexistent swap-page\n");
		return;
	}
	p = & swap_info[type];
	offset = SWP_OFFSET(entry);
	if (offset >= p->max) {
		printk("swap_free: weirdness\n");
		return;
	}
	if (!(p->flags & SWP_USED)) {
		printk("Trying to free swap from unused swap-device\n");
		return;
	}
	while (set_bit(offset,p->swap_lockmap))
		sleep_on(&lock_queue);
	if (offset < p->lowest_bit)
		p->lowest_bit = offset;
	if (offset > p->highest_bit)
		p->highest_bit = offset;
	if (!p->swap_map[offset])
		printk("swap_free: swap-space map bad (entry %08lx)\n",entry);
	else
		if (!--p->swap_map[offset])
			nr_swap_pages++;
	if (!clear_bit(offset,p->swap_lockmap))
		printk("swap_free: lock already cleared\n");
	wake_up(&lock_queue);
}

void swap_in(unsigned long *table_ptr)
{
	unsigned long entry;
	unsigned long page;

	entry = *table_ptr;
	if (PAGE_PRESENT & entry) {
		printk("trying to swap in present page\n");
		return;
	}
	if (!entry) {
		printk("No swap page in swap_in\n");
		return;
	}
	if (SWP_TYPE(entry) == SHM_SWP_TYPE) {
		shm_no_page ((unsigned long *) table_ptr);
		return;
	}
	if (!(page = get_free_page(GFP_KERNEL))) {
		oom(current);
		page = BAD_PAGE;
	} else	
		read_swap_page(entry, (char *) page);
	if (*table_ptr != entry) {
		free_page(page);
		return;
	}
	*table_ptr = page | (PAGE_DIRTY | PAGE_PRIVATE);
	swap_free(entry);
}

static inline int try_to_swap_out(unsigned long * table_ptr)
{
	int i;
	unsigned long page;
	unsigned long entry;

	page = *table_ptr;
	if (!(PAGE_PRESENT & page))
		return 0;
	if (page >= high_memory)
		return 0;
	if (mem_map[MAP_NR(page)] & MAP_PAGE_RESERVED)
		return 0;
	if (PAGE_ACCESSED & page) {
		*table_ptr &= ~PAGE_ACCESSED;
		return 0;
	}
	for (i = 0; i < NR_LAST_FREE_PAGES; i++)
		if (last_free_pages[i] == (page & PAGE_MASK))
			return 0;
	if (PAGE_DIRTY & page) {
		page &= PAGE_MASK;
		if (mem_map[MAP_NR(page)] != 1)
			return 0;
		if (!(entry = get_swap_page()))
			return 0;
		*table_ptr = entry;
		invalidate();
		write_swap_page(entry, (char *) page);
		free_page(page);
		return 1;
	}
	page &= PAGE_MASK;
	*table_ptr = 0;
	invalidate();
	free_page(page);
	return 1 + mem_map[MAP_NR(page)];
}

/*
 * sys_idle() does nothing much: it just searches for likely candidates for
 * swapping out or forgetting about. This speeds up the search when we
 * actually have to swap.
 */
asmlinkage int sys_idle(void)
{
	need_resched = 1;
	return 0;
}

/*
 * A new implementation of swap_out().  We do not swap complete processes,
 * but only a small number of blocks, before we continue with the next
 * process.  The number of blocks actually swapped is determined on the
 * number of page faults, that this process actually had in the last time,
 * so we won't swap heavily used processes all the time ...
 *
 * Note: the priority argument is a hint on much CPU to waste with the
 *       swap block search, not a hint, of how much blocks to swap with
 *       each process.
 *
 * (C) 1993 Kai Petzke, [e-mail]
 */
#ifdef NEW_SWAP
/*
 * These are the miminum and maximum number of pages to swap from one process,
 * before proceeding to the next:
 */
#define SWAP_MIN	4
#define SWAP_MAX	32

/*
 * The actual number of pages to swap is determined as:
 * SWAP_RATIO / (number of recent major page faults)
 */
#define SWAP_RATIO	128

static int swap_out(unsigned int priority)
{
    static int swap_task;
    int table;
    int page;
    long pg_table;
    int loop;
    int counter = NR_TASKS * 2 >> priority;
    struct task_struct *p;

    counter = NR_TASKS * 2 >> priority;
    for(; counter >= 0; counter--, swap_task++) {
	/*
	 * Check that swap_task is suitable for swapping.  If not, look for
	 * the next suitable process.
	 */
	loop = 0;
	while(1) {
	    if(swap_task >= NR_TASKS) {
		swap_task = 1;
		if(loop)
		    /* all processes are unswappable or already swapped out */
		    return 0;
		loop = 1;
	    }

	    p = task[swap_task];
	    if(p && p->swappable && p->rss)
		break;

	    swap_task++;
	}

	/*
	 * Determine the number of pages to swap from this process.
	 */
	if(! p -> swap_cnt) {
	    p->dec_flt = (p->dec_flt * 3) / 4 + p->maj_flt - p->old_maj_flt;
	    p->old_maj_flt = p->maj_flt;

	    if(p->dec_flt >= SWAP_RATIO / SWAP_MIN) {
		p->dec_flt = SWAP_RATIO / SWAP_MIN;
		p->swap_cnt = SWAP_MIN;
	    } else if(p->dec_flt <= SWAP_RATIO / SWAP_MAX)
		p->swap_cnt = SWAP_MAX;
	    else
		p->swap_cnt = SWAP_RATIO / p->dec_flt;
	}

	/*
	 * Go through process' page directory.
	 */
	for(table = p->swap_table; table < 1024; table++) {
	    pg_table = ((unsigned long *) p->tss.cr3)[table];
	    if(pg_table >= high_memory)
		    continue;
	    if(mem_map[MAP_NR(pg_table)] & MAP_PAGE_RESERVED)
		    continue;
	    if(!(PAGE_PRESENT & pg_table)) {
		    printk("swap_out: bad page-table at pg_dir[%d]: %08lx\n",
			    table, pg_table);
		    ((unsigned long *) p->tss.cr3)[table] = 0;
		    continue;
	    }
	    pg_table &= 0xfffff000;

	    /*
	     * Go through this page table.
	     */
	    for(page = p->swap_page; page < 1024; page++) {
		switch(try_to_swap_out(page + (unsigned long *) pg_table)) {
		    case 0:
			break;

		    case 1:
			p->rss--;
			/* continue with the following page the next time */
			p->swap_table = table;
			p->swap_page  = page + 1;
			if((--p->swap_cnt) == 0)
			    swap_task++;
			return 1;

		    default:
			p->rss--;
			break;
		}
	    }

	    p->swap_page = 0;
	}

	/*
	 * Finish work with this process, if we reached the end of the page
	 * directory.  Mark restart from the beginning the next time.
	 */
	p->swap_table = 0;
    }
    return 0;
}

#else /* old swapping procedure */

/*
 * Go through the page tables, searching for a user page that
 * we can swap out.
 * 
 * We now check that the process is swappable (normally only 'init'
 * is un-swappable), allowing high-priority processes which cannot be
 * swapped out (things like user-level device drivers (Not implemented)).
 */
static int swap_out(unsigned int priority)
{
	static int swap_task = 1;
	static int swap_table = 0;
	static int swap_page = 0;
	int counter = NR_TASKS*8;
	int pg_table;
	struct task_struct * p;

	counter >>= priority;
check_task:
	if (counter-- < 0)
		return 0;
	if (swap_task >= NR_TASKS) {