mm/swap

/*
 *  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;

//交换信息结构
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,};

//读写交换页
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 ");
        return;
    }
    p = &swap_info[type];
    offset = SWP_OFFSET(entry);
    if (offset >= p->max) {
        printk("rw_swap_page: weirdness ");
        return;
    }
    if (!(p->flags & SWP_USED)) {
        printk("Trying to swap to unused swap-device ");
        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 ");
                return;
            }
        ll_rw_swap_file(rw,p->swap_file->i_dev, zones, i,buf);
    } else
        printk("re_swap_page: no swap file or device ");
    if (offset && !clear_bit(offset,p->swap_lockmap))
        printk("rw_swap_page: lock already cleared ");
    wake_up(&lock_queue);
}

//获取交换页
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;
}

//复制交换页
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 ");
        return 0;
    }
    p = type + swap_info;
    if (offset >= p->max) {
        printk("swap_free: weirdness ");
        return 0;
    }
    if (!p->swap_map[offset]) {
        printk("swap_duplicate: trying to duplicate unused page ");
        return 0;
    }
    p->swap_map[offset]++;
    return entry;
}

//释放
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 ");
        return;
    }
    p = & swap_info[type];
    offset = SWP_OFFSET(entry);
    if (offset >= p->max) {
        printk("swap_free: weirdness ");
        return;
    }
    if (!(p->flags & SWP_USED)) {
        printk("Trying to free swap from unused swap-device ");
        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) ",entry);
    else
        if (!--p->swap_map[offset])
            nr_swap_pages++;
    if (!clear_bit(offset,p->swap_lockmap))
        printk("swap_free: lock already cleared ");
    wake_up(&lock_queue);
}

//交换入
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 ");
        return;
    }
    if (!entry) {
        printk("No swap page in swap_in ");
        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);
}

//试图交换出
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.
 */
 //空闲
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, wpp@marie.physik.tu-berlin.de
 */
#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

//交换出
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 ",
                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) {
        swap_task = 1;
        goto check_task;
    }
    p = task[swap_task];
    if (!p || !p->swappable) {
        swap_task++;
        goto check_task;
    }
check_dir:
    if (swap_table >= PTRS_PER_PAGE) {
        swap_table = 0;
        swap_task++;
        goto check_task;
    }
    pg_table = ((unsigned long *) p->tss.cr3)[swap_table];
    if (pg_table >= high_memory || (mem_map[MAP_NR(pg_table)] & MAP_PAGE_RESERVED)) {
        swap_table++;
        goto check_dir;
    }
    if (!(PAGE_PRESENT & pg_table)) {
        printk("bad page-table at pg_dir[%d]: %08x ",
            swap_table,pg_table);
        ((unsigned long *) p->tss.cr3)[swap_table] = 0;
        swap_table++;
        goto check_dir;
    }
    pg_table &= PAGE_MASK;
check_table:
    if (swap_page >= PTRS_PER_PAGE) {
        swap_page = 0;
        swap_table++;
        goto check_dir;
    }
    switch (try_to_swap_out(swap_page + (unsigned long *) pg_table)) {
        case 0: break;
        case 1: p->rss--; return 1;
        default: p->rss--;
    }
    swap_page++;
    goto check_table;
}

#endif

//尝试释放页面
static int try_to_free_page(void)
{
    int i=6;

    while (i--) {
        if (shrink_buffers(i))
            return 1;
        if (shm_swap(i))
            return 1;
        if (swap_out(i))
            return 1;
    }
    return 0;
}

/*
 * Note that this must be atomic, or bad things will happen when
 * pages are requested in interrupts (as malloc can do). Thus the
 * cli/sti's.
 */
 //添加内存队列
static inline void add_mem_queue(unsigned long addr, unsigned long * queue)
{
    addr &= PAGE_MASK;
    *(unsigned long *) addr = *queue;
    *queue = addr;
}

/*
 * Free_page() adds the page to the free lists. This is optimized for
 * fast normal cases (no error jumps taken normally).
 *
 * The way to optimize jumps for gcc-2.2.2 is to:
 *  - select the "normal" case and put it inside the if () { XXX }
 *  - no else-statements if you can avoid them
 *
 * With the above two rules, you get a straight-line execution path
 * for the normal case, giving better asm-code.
 */
 //释放页面
void free_page(unsigned long addr)
{
    if (addr < high_memory) {
        unsigned short * map = mem_map + MAP_NR(addr);

        if (*map) {
            if (!(*map & MAP_PAGE_RESERVED)) {
                unsigned long flag;

                save_flags(flag);
                cli();
                if (!--*map) {
                    if (nr_secondary_pages < MAX_SECONDARY_PAGES) {
                        add_mem_queue(addr,&secondary_page_list);
                        nr_secondary_pages++;
                        restore_flags(flag);
                        return;
                    }
                    add_mem_queue(addr,&free_page_list);
                    nr_free_pages++;
                }
                restore_flags(flag);
            }
            return;
        }
        printk("Trying to free free memory (%08lx): memory probabably corrupted ",addr);
        printk("PC = %08lx ",*(((unsigned long *)&addr)-1));
        return;
    }
}

/*
 * This is one ugly macro, but it simplifies checking, and makes
 * this speed-critical place reasonably fast, especially as we have
 * to do things with the interrupt flag etc.
 *
 * Note that this #define is heavily optimized to give fast code
 * for the normal case - the if-statements are ordered so that gcc-2.2.2
 * will make *no* jumps for the normal code. Don't touch unless you
 * know what you are doing.
 */
 //从内存队列中移除
#define REMOVE_FROM_MEM_QUEUE(queue,nr)
    cli();
    if ((result = queue) != 0) {
        if (!(result & ~PAGE_MASK) && result < high_memory) {
            queue = *(unsigned long *) result;
            if (!mem_map[MAP_NR(result)]) {
                mem_map[MAP_NR(result)] = 1;
                nr--;
last_free_pages[index = (index + 1) & (NR_LAST_FREE_PAGES - 1)] = result;
                restore_flags(flag);
                return result;
            }
            printk("Free page %08lx has mem_map = %d ",
                result,mem_map[MAP_NR(result)]);
        } else
            printk("Result = 0x%08lx - memory map destroyed ", result);
        queue = 0;
        nr = 0;
    } else if (nr) {
        printk(#nr " is %d, but " #queue " is empty ",nr);
        nr = 0;
    }
    restore_flags(flag)

/*
 * Get physical address of first (actually last :-) free page, and mark it
 * used. If no free pages left, return 0.
 *
 * Note that this is one of the most heavily called functions in the kernel,
 * so it's a bit timing-critical (especially as we have to disable interrupts
 * in it). See the above macro which does most of the work, and which is
 * optimized for a fast normal path of execution.
 */
 //获取空闲页
unsigned long __get_free_page(int priority)
{
    extern unsigned long intr_count;
    unsigned long result, flag;
    static unsigned long index = 0;

    /* this routine can be called at interrupt time via
       malloc.  We want to make sure that the critical
       sections of code have interrupts disabled. -RAB
       Is this code reentrant? */

    if (intr_count && priority != GFP_ATOMIC) {
        printk("gfp called nonatomically from interrupt %08lx ",
            ((unsigned long *)&priority)[-1]);
        priority = GFP_ATOMIC;
    }
    save_flags(flag);
repeat:
    REMOVE_FROM_MEM_QUEUE(free_page_list,nr_free_pages);
    if (priority == GFP_BUFFER)
        return 0;
    if (priority != GFP_ATOMIC)
        if (try_to_free_page())
            goto repeat;
    REMOVE_FROM_MEM_QUEUE(secondary_page_list,nr_secondary_pages);
    return 0;
}

/*
 * Trying to stop swapping from a file is fraught with races, so
 * we repeat quite a bit here when we have to pause. swapoff()
 * isn't exactly timing-critical, so who cares?
 */
 //尝试取消使用
static int try_to_unuse(unsigned int type)
{
    int nr, pgt, pg;
    unsigned long page, *ppage;
    unsigned long tmp = 0;
    struct task_struct *p;

    nr = 0;
/*
 * When we have to sleep, we restart the whole algorithm from the same
 * task we stopped in. That at least rids us of all races.
 */
repeat:
    for (; nr < NR_TASKS ; nr++) {
        p = task[nr];
        if (!p)
            continue;
        for (pgt = 0 ; pgt < PTRS_PER_PAGE ; pgt++) {
            ppage = pgt + ((unsigned long *) p->tss.cr3);
            page = *ppage;
            if (!page)
                continue;
            if (!(page & PAGE_PRESENT) || (page >= high_memory))
                continue;
            if (mem_map[MAP_NR(page)] & MAP_PAGE_RESERVED)
                continue;
            ppage = (unsigned long *) (page & PAGE_MASK);    
            for (pg = 0 ; pg < PTRS_PER_PAGE ; pg++,ppage++) {
                page = *ppage;
                if (!page)
                    continue;
                if (page & PAGE_PRESENT)
                    continue;
                if (SWP_TYPE(page) != type)
                    continue;
                if (!tmp) {
                    if (!(tmp = __get_free_page(GFP_KERNEL)))
                        return -ENOMEM;
                    goto repeat;
                }
                read_swap_page(page, (char *) tmp);
                if (*ppage == page) {
                    *ppage = tmp | (PAGE_DIRTY | PAGE_PRIVATE);
                    ++p->rss;
                    swap_free(page);
                    tmp = 0;
                }
                goto repeat;
            }
        }
    }
    free_page(tmp);
    return 0;
}

//关闭交换
asmlinkage int sys_swapoff(const char * specialfile)
{
    struct swap_info_struct * p;
    struct inode * inode;
    unsigned int type;
    int i;

    if (!suser())
        return -EPERM;
    i = namei(specialfile,&inode);
    if (i)
        return i;
    p = swap_info;
    for (type = 0 ; type < nr_swapfiles ; type++,p++) {
        if ((p->flags & SWP_WRITEOK) != SWP_WRITEOK)
            continue;
        if (p->swap_file) {
            if (p->swap_file == inode)
                break;
        } else {
            if (!S_ISBLK(inode->i_mode))
                continue;
            if (p->swap_device == inode->i_rdev)
                break;
        }
    }
    iput(inode);
    if (type >= nr_swapfiles)
        return -EINVAL;
    p->flags = SWP_USED;
    i = try_to_unuse(type);
    if (i) {
        p->flags = SWP_WRITEOK;
        return i;
    }
    nr_swap_pages -= p->pages;
    iput(p->swap_file);
    p->swap_file = NULL;
    p->swap_device = 0;
    vfree(p->swap_map);
    p->swap_map = NULL;
    free_page((long) p->swap_lockmap);
    p->swap_lockmap = NULL;
    p->flags = 0;
    return 0;
}

/*
 * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
 *
 * The swapon system call
 */
 //打开交换
asmlinkage int sys_swapon(const char * specialfile)
{
    struct swap_info_struct * p;
    struct inode * swap_inode;
    unsigned int type;
    int i,j;
    int error;

    if (!suser())
        return -EPERM;
    p = swap_info;
    for (type = 0 ; type < nr_swapfiles ; type++,p++)
        if (!(p->flags & SWP_USED))
            break;
    if (type >= MAX_SWAPFILES)
        return -EPERM;
    if (type >= nr_swapfiles)
        nr_swapfiles = type+1;
    p->flags = SWP_USED;
    p->swap_file = NULL;
    p->swap_device = 0;
    p->swap_map = NULL;
    p->swap_lockmap = NULL;
    p->lowest_bit = 0;
    p->highest_bit = 0;
    p->max = 1;
    error = namei(specialfile,&swap_inode);
    if (error)
        goto bad_swap;
    error = -EBUSY;
    if (swap_inode->i_count != 1)
        goto bad_swap;
    error = -EINVAL;
    if (S_ISBLK(swap_inode->i_mode)) {
        p->swap_device = swap_inode->i_rdev;
        iput(swap_inode);
        error = -ENODEV;
        if (!p->swap_device)
            goto bad_swap;
        error = -EBUSY;
        for (i = 0 ; i < nr_swapfiles ; i++) {
            if (i == type)
                continue;
            if (p->swap_device == swap_info[i].swap_device)
                goto bad_swap;
        }
    } else if (S_ISREG(swap_inode->i_mode))
        p->swap_file = swap_inode;
    else
        goto bad_swap;
    p->swap_lockmap = (unsigned char *) get_free_page(GFP_USER);
    if (!p->swap_lockmap) {
        printk("Unable to start swapping: out of memory :-) ");
        error = -ENOMEM;
        goto bad_swap;
    }
    read_swap_page(SWP_ENTRY(type,0), (char *) p->swap_lockmap);
    if (memcmp("SWAP-SPACE",p->swap_lockmap+4086,10)) {
        printk("Unable to find swap-space signature ");
        error = -EINVAL;
        goto bad_swap;
    }
    memset(p->swap_lockmap+PAGE_SIZE-10,0,10);
    j = 0;
    p->lowest_bit = 0;
    p->highest_bit = 0;
    for (i = 1 ; i < 8*PAGE_SIZE ; i++) {
        if (test_bit(i,p->swap_lockmap)) {
            if (!p->lowest_bit)
                p->lowest_bit = i;
            p->highest_bit = i;
            p->max = i+1;
            j++;
        }
    }
    if (!j) {
        printk("Empty swap-file ");
        error = -EINVAL;
        goto bad_swap;
    }
    p->swap_map = (unsigned char *) vmalloc(p->max);
    if (!p->swap_map) {
        error = -ENOMEM;
        goto bad_swap;
    }
    for (i = 1 ; i < p->max ; i++) {
        if (test_bit(i,p->swap_lockmap))
            p->swap_map[i] = 0;
        else
            p->swap_map[i] = 0x80;
    }
    p->swap_map[0] = 0x80;
    memset(p->swap_lockmap,0,PAGE_SIZE);
    p->flags = SWP_WRITEOK;
    p->pages = j;
    nr_swap_pages += j;
    printk("Adding Swap: %dk swap-space ",j<<2);
    return 0;
bad_swap:
    free_page((long) p->swap_lockmap);
    vfree(p->swap_map);
    iput(p->swap_file);
    p->swap_device = 0;
    p->swap_file = NULL;
    p->swap_map = NULL;
    p->swap_lockmap = NULL;
    p->flags = 0;
    return error;
}
//交换信息
void si_swapinfo(struct sysinfo *val)
{
    unsigned int i, j;

    val->freeswap = val->totalswap = 0;
    for (i = 0; i < nr_swapfiles; i++) {
        if (!(swap_info[i].flags & SWP_USED))
            continue;
        for (j = 0; j < swap_info[i].max; ++j)
            switch (swap_info[i].swap_map[j]) {
                case 128:
                    continue;
                case 0:
                    ++val->freeswap;
                default:
                    ++val->totalswap;
            }
    }
    val->freeswap <<= PAGE_SHIFT;
    val->totalswap <<= PAGE_SHIFT;
    return;
}