path: root/xen-2.4.16/common/page_alloc.c

/******************************************************************************
 * page_alloc.c
 * 
 * Simple buddy allocator for Xenoserver hypervisor.
 * 
 * Copyright (c) 2002 K A Fraser
 */

#include <xeno/config.h>
#include <xeno/init.h>
#include <xeno/types.h>
#include <xeno/lib.h>
#include <asm/page.h>
#include <xeno/spinlock.h>


static spinlock_t alloc_lock = SPIN_LOCK_UNLOCKED;


/*********************
 * ALLOCATION BITMAP
 *  One bit per page of memory. Bit set => page is allocated.
 */

static unsigned long *alloc_bitmap;
#define PAGES_PER_MAPWORD (sizeof(unsigned long) * 8)

#define allocated_in_map(_pn) \
(alloc_bitmap[(_pn)/PAGES_PER_MAPWORD] & (1<<((_pn)&(PAGES_PER_MAPWORD-1))))


/*
 * Hint regarding bitwise arithmetic in map_{alloc,free}:
 *  -(1<<n)  sets all bits >= n. 
 *  (1<<n)-1 sets all bits <  n.
 * Variable names in map_{alloc,free}:
 *  *_idx == Index into `alloc_bitmap' array.
 *  *_off == Bit offset within an element of the `alloc_bitmap' array.
 */

static void map_alloc(unsigned long first_page, unsigned long nr_pages)
{
    unsigned long start_off, end_off, curr_idx, end_idx;

    curr_idx  = first_page / PAGES_PER_MAPWORD;
    start_off = first_page & (PAGES_PER_MAPWORD-1);
    end_idx   = (first_page + nr_pages) / PAGES_PER_MAPWORD;
    end_off   = (first_page + nr_pages) & (PAGES_PER_MAPWORD-1);

    if ( curr_idx == end_idx )
    {
        alloc_bitmap[curr_idx] |= ((1<<end_off)-1) & -(1<<start_off);
    }
    else 
    {
        alloc_bitmap[curr_idx] |= -(1<<start_off);
        while ( ++curr_idx < end_idx ) alloc_bitmap[curr_idx] = ~0L;
        alloc_bitmap[curr_idx] |= (1<<end_off)-1;
    }
}


static void map_free(unsigned long first_page, unsigned long nr_pages)
{
    unsigned long start_off, end_off, curr_idx, end_idx;

    curr_idx = first_page / PAGES_PER_MAPWORD;
    start_off = first_page & (PAGES_PER_MAPWORD-1);
    end_idx   = (first_page + nr_pages) / PAGES_PER_MAPWORD;
    end_off   = (first_page + nr_pages) & (PAGES_PER_MAPWORD-1);

    if ( curr_idx == end_idx )
    {
        alloc_bitmap[curr_idx] &= -(1<<end_off) | ((1<<start_off)-1);
    }
    else 
    {
        alloc_bitmap[curr_idx] &= (1<<start_off)-1;
        while ( ++curr_idx != end_idx ) alloc_bitmap[curr_idx] = 0;
        alloc_bitmap[curr_idx] &= -(1<<end_off);
    }
}



/*************************
 * BINARY BUDDY ALLOCATOR
 */

typedef struct chunk_head_st chunk_head_t;
typedef struct chunk_tail_st chunk_tail_t;

struct chunk_head_st {
    chunk_head_t  *next;
    chunk_head_t **pprev;
    int            level;
};

struct chunk_tail_st {
    int level;
};

/* Linked lists of free chunks of different powers-of-two in size. */
#define FREELIST_SIZE ((sizeof(void*)<<3)-PAGE_SHIFT)
static chunk_head_t *free_list[FREELIST_SIZE];
static chunk_head_t  free_tail[FREELIST_SIZE];
#define FREELIST_EMPTY(_l) ((_l)->next == NULL)

#define round_pgdown(_p)  ((_p)&PAGE_MASK)
#define round_pgup(_p)    (((_p)+(PAGE_SIZE-1))&PAGE_MASK)


/* Initialise allocator, placing addresses [@min,@max] in free pool. */
void __init init_page_allocator(unsigned long min, unsigned long max)
{
    int i;
    unsigned long range, bitmap_size;
    chunk_head_t *ch;
    chunk_tail_t *ct;

    for ( i = 0; i < FREELIST_SIZE; i++ )
    {
        free_list[i]       = &free_tail[i];
        free_tail[i].pprev = &free_list[i];
        free_tail[i].next  = NULL;
    }

    min = round_pgup  (min);
    max = round_pgdown(max);

    /* Allocate space for the allocation bitmap. */
    bitmap_size  = (max+1) >> (PAGE_SHIFT+3);
    bitmap_size  = round_pgup(bitmap_size);
    alloc_bitmap = (unsigned long *)__va(min);
    min         += bitmap_size;
    range        = max - min;

    /* All allocated by default. */
    memset(alloc_bitmap, ~0, bitmap_size);
    /* Free up the memory we've been given to play with. */
    map_free(min>>PAGE_SHIFT, range>>PAGE_SHIFT);
    
    /* The buddy lists are addressed in high memory. */
    min += PAGE_OFFSET;
    max += PAGE_OFFSET;

    while ( range != 0 )
    {
        /*
         * Next chunk is limited by alignment of min, but also
         * must not be bigger than remaining range.
         */
        for ( i = PAGE_SHIFT; (1<<(i+1)) <= range; i++ )
            if ( min & (1<<i) ) break;

        ch = (chunk_head_t *)min;
        min   += (1<<i);
        range -= (1<<i);
        ct = (chunk_tail_t *)min-1;
        i -= PAGE_SHIFT;
        ch->level       = i;
        ch->next        = free_list[i];
        ch->pprev       = &free_list[i];
        ch->next->pprev = &ch->next;
        free_list[i]    = ch;
        ct->level       = i;
    }
}


/* Allocate 2^@order contiguous pages. */
unsigned long __get_free_pages(int mask, int order)
{
    int i;
    chunk_head_t *alloc_ch, *spare_ch;
    chunk_tail_t            *spare_ct;
    unsigned long           flags;

    spin_lock_irqsave(&alloc_lock, flags);


    /* Find smallest order which can satisfy the request. */
    for ( i = order; i < FREELIST_SIZE; i++ ) {
	if ( !FREELIST_EMPTY(free_list[i]) ) 
	    break;
    }

    if ( i == FREELIST_SIZE )
    {
        printk("Cannot handle page request order %d!\n", order);
	return NULL; 
    }
 
    /* Unlink a chunk. */
    alloc_ch = free_list[i];
    free_list[i] = alloc_ch->next;
    alloc_ch->next->pprev = alloc_ch->pprev;

    /* We may have to break the chunk a number of times. */
    while ( i != order )
    {
        /* Split into two equal parts. */
        i--;
        spare_ch = (chunk_head_t *)((char *)alloc_ch + (1<<(i+PAGE_SHIFT)));
        spare_ct = (chunk_tail_t *)((char *)spare_ch + (1<<(i+PAGE_SHIFT)))-1;

        /* Create new header for spare chunk. */
        spare_ch->level = i;
        spare_ch->next  = free_list[i];
        spare_ch->pprev = &free_list[i];
        spare_ct->level = i;

        /* Link in the spare chunk. */
        spare_ch->next->pprev = &spare_ch->next;
        free_list[i] = spare_ch;
    }
    
    map_alloc(__pa(alloc_ch)>>PAGE_SHIFT, 1<<order);

    spin_unlock_irqrestore(&alloc_lock, flags);

    return((unsigned long)alloc_ch);
}


/* Free 2^@order pages at location @p. */
void __free_pages(unsigned long p, int order)
{
    unsigned long size = 1 << (order + PAGE_SHIFT);
    chunk_head_t *ch;
    chunk_tail_t *ct;
    unsigned long flags;
    unsigned long pagenr = __pa(p) >> PAGE_SHIFT;

    spin_lock_irqsave(&alloc_lock, flags);

    map_free(pagenr, 1<<order);
    
    /* Merge chunks as far as possible. */
    for ( ; ; )
    {
        if ( (p & size) )
        {
            /* Merge with predecessor block? */
            if ( allocated_in_map(pagenr-1) ) break;
            ct = (chunk_tail_t *)p - 1;
            if ( ct->level != order ) break;
            ch = (chunk_head_t *)(p - size);
            p -= size;
        }
        else
        {
            /* Merge with successor block? */
            if ( allocated_in_map(pagenr+(1<<order)) ) break;
            ch = (chunk_head_t *)(p + size);
            if ( ch->level != order ) break;
        }
        
        /* Okay, unlink the neighbour. */
        *ch->pprev = ch->next;
        ch->next->pprev = ch->pprev;

        order++;
        size <<= 1;
    }

    /* Okay, add the final chunk to the appropriate free list. */
    ch = (chunk_head_t *)p;
    ct = (chunk_tail_t *)(p+size)-1;
    ct->level = order;
    ch->level = order;
    ch->pprev = &free_list[order];
    ch->next  = free_list[order];
    ch->next->pprev = &ch->next;
    free_list[order] = ch;

    spin_unlock_irqrestore(&alloc_lock, flags);
}