Cosmos/source/Playgrounds/Ben/SOOOS/Code/TextFile1.txt

/*
 * Initialise allocator, placing addresses [@min,@max] in free pool.
 * @min and @max are PHYSICAL addresses.
 */
static void 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_head[i]       = &free_tail[i];
        free_tail[i].pprev = &free_head[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 *)to_virt(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 += VIRT_START;
    max += VIRT_START;

    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_head[i];
        ch->pprev       = &free_head[i];
        ch->next->pprev = &ch->next;
        free_head[i]    = ch;
        ct->level       = i;
    }
}


/* Allocate 2^@order contiguous pages. Returns a VIRTUAL address. */
unsigned long alloc_pages(int order)
{
    int i;
    chunk_head_t *alloc_ch, *spare_ch;
    chunk_tail_t            *spare_ct;


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

    if ( i == FREELIST_SIZE ) goto no_memory;
 
    /* Unlink a chunk. */
    alloc_ch = free_head[i];
    free_head[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_head[i];
        spare_ch->pprev = &free_head[i];
        spare_ct->level = i;

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

    return((unsigned long)alloc_ch);

 no_memory:

    printk("Cannot handle page request order %d!\n", order);

    return 0;
}

void free_pages(void *pointer, int order)
{
    chunk_head_t *freed_ch, *to_merge_ch;
    chunk_tail_t *freed_ct;
    unsigned long mask;
    
    /* First free the chunk */
    map_free(virt_to_pfn(pointer), 1 << order);
    
    /* Create free chunk */
    freed_ch = (chunk_head_t *)pointer;
    freed_ct = (chunk_tail_t *)((char *)pointer + (1<<(order + PAGE_SHIFT)))-1;
    
    /* Now, possibly we can conseal chunks together */
    while(order < FREELIST_SIZE)
    {
        mask = 1 << (order + PAGE_SHIFT);
        if((unsigned long)freed_ch & mask) 
        {
            to_merge_ch = (chunk_head_t *)((char *)freed_ch - mask);
            if(allocated_in_map(virt_to_pfn(to_merge_ch)) ||
                    to_merge_ch->level != order)
                break;
            
            /* Merge with predecessor */
            freed_ch = to_merge_ch;   
        }
        else 
        {
            to_merge_ch = (chunk_head_t *)((char *)freed_ch + mask);
            if(allocated_in_map(virt_to_pfn(to_merge_ch)) ||
                    to_merge_ch->level != order)
                break;
            
            /* Merge with successor */
            freed_ct = (chunk_tail_t *)((char *)to_merge_ch + mask) - 1;
        }
        
        /* We are commited to merging, unlink the chunk */
        *(to_merge_ch->pprev) = to_merge_ch->next;
        to_merge_ch->next->pprev = to_merge_ch->pprev;
        
        order++;
    }

    /* Link the new chunk */
    freed_ch->level = order;
    freed_ch->next  = free_head[order];
    freed_ch->pprev = &free_head[order];
    freed_ct->level = order;
    
    freed_ch->next->pprev = &freed_ch->next;
    free_head[order] = freed_ch;   
   
}