__alloc_bootmem_core

分配页内存底层函数

/*
 * We 'merge' subsequent allocations to save space. We might 'lose'
 * some fraction of a page if allocations cannot be satisfied due to
 * size constraints on boxes where there is physical RAM space
 * fragmentation - in these cases (mostly large memory boxes) this
 * is not a problem.
 *
 * On low memory boxes we get it right in 100% of the cases.
 *
 * alignment has to be a power of 2 value.
 *
 * NOTE:  This function is _not_ reentrant.
 */
static void * __init
__alloc_bootmem_core(struct bootmem_data *bdata, unsigned long size,
		unsigned long align, unsigned long goal)
{
	unsigned long offset, remaining_size, areasize, preferred;
	unsigned long i, start = 0, incr, eidx;
	void *ret;

	if(!size) {
		printk("__alloc_bootmem_core(): zero-sized request\n");
		BUG();
	}
	BUG_ON(align & (align-1));

	eidx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
	offset = 0;
	if (align &&
	    (bdata->node_boot_start & (align - 1UL)) != 0)
		offset = (align - (bdata->node_boot_start & (align - 1UL)));
	offset >>= PAGE_SHIFT;

	/*
	 * We try to allocate bootmem pages above 'goal'
	 * first, then we try to allocate lower pages.
	 */
	if (goal && (goal >= bdata->node_boot_start) && 
	    ((goal >> PAGE_SHIFT) < bdata->node_low_pfn)) {
		preferred = goal - bdata->node_boot_start;

		if (bdata->last_success >= preferred)
			preferred = bdata->last_success;
	} else
		preferred = 0;

	preferred = ((preferred + align - 1) & ~(align - 1)) >> PAGE_SHIFT;
	preferred += offset;
	areasize = (size+PAGE_SIZE-1)/PAGE_SIZE;
	incr = align >> PAGE_SHIFT ? : 1;

restart_scan:
	for (i = preferred; i < eidx; i += incr) {
		unsigned long j;
		i = find_next_zero_bit(bdata->node_bootmem_map, eidx, i);
		i = ALIGN(i, incr);
		if (test_bit(i, bdata->node_bootmem_map))
			continue;
		for (j = i + 1; j < i + areasize; ++j) {
			if (j >= eidx)
				goto fail_block;
			if (test_bit (j, bdata->node_bootmem_map))
				goto fail_block;
		}
		start = i;
		goto found;
	fail_block:
		i = ALIGN(j, incr);
	}

	if (preferred > offset) {
		preferred = offset;
		goto restart_scan;
	}
	return NULL;

found:
	bdata->last_success = start << PAGE_SHIFT;
	BUG_ON(start >= eidx);

	/*
	 * Is the next page of the previous allocation-end the start
	 * of this allocation's buffer? If yes then we can 'merge'
	 * the previous partial page with this allocation.
	 */
	if (align < PAGE_SIZE &&
	    bdata->last_offset && bdata->last_pos+1 == start) {
		offset = (bdata->last_offset+align-1) & ~(align-1);
		BUG_ON(offset > PAGE_SIZE);
		remaining_size = PAGE_SIZE-offset;
		if (size < remaining_size) {
			areasize = 0;
			/* last_pos unchanged */
			bdata->last_offset = offset+size;
			ret = phys_to_virt(bdata->last_pos*PAGE_SIZE + offset +
						bdata->node_boot_start);
		} else {
			remaining_size = size - remaining_size;
			areasize = (remaining_size+PAGE_SIZE-1)/PAGE_SIZE;
			ret = phys_to_virt(bdata->last_pos*PAGE_SIZE + offset +
						bdata->node_boot_start);
			bdata->last_pos = start+areasize-1;
			bdata->last_offset = remaining_size;
		}
		bdata->last_offset &= ~PAGE_MASK;
	} else {
		bdata->last_pos = start + areasize - 1;
		bdata->last_offset = size & ~PAGE_MASK;
		ret = phys_to_virt(start * PAGE_SIZE + bdata->node_boot_start);
	}

	/*
	 * Reserve the area now:
	 */
	for (i = start; i < start+areasize; i++)
		if (unlikely(test_and_set_bit(i, bdata->node_bootmem_map)))
			BUG();
	memset(ret, 0, size);
	return ret;
}

static unsigned long __init free_all_bootmem_core(pg_data_t *pgdat)
{
	struct page *page;
	bootmem_data_t *bdata = pgdat->bdata;
	unsigned long i, count, total = 0;
	unsigned long idx;
	unsigned long *map; 
	int gofast = 0;

	BUG_ON(!bdata->node_bootmem_map);

	count = 0;
	/* first extant page of the node */
	page = virt_to_page(phys_to_virt(bdata->node_boot_start));
	idx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
	map = bdata->node_bootmem_map;
	/* Check physaddr is O(LOG2(BITS_PER_LONG)) page aligned */
	if (bdata->node_boot_start == 0 ||
	    ffs(bdata->node_boot_start) - PAGE_SHIFT > ffs(BITS_PER_LONG))
		gofast = 1;
	for (i = 0; i < idx; ) {
		unsigned long v = ~map[i / BITS_PER_LONG];
		if (gofast && v == ~0UL) {
			int j, order;

			count += BITS_PER_LONG;
			__ClearPageReserved(page);
			order = ffs(BITS_PER_LONG) - 1;
			set_page_refs(page, order);
			for (j = 1; j < BITS_PER_LONG; j++) {
				if (j + 16 < BITS_PER_LONG)
					prefetchw(page + j + 16);
				__ClearPageReserved(page + j);
			}
			__free_pages(page, order);
			i += BITS_PER_LONG;
			page += BITS_PER_LONG;
		} else if (v) {
			unsigned long m;
			for (m = 1; m && i < idx; m<<=1, page++, i++) {
				if (v & m) {
					count++;
					__ClearPageReserved(page);
					set_page_refs(page, 0);
					__free_page(page);
				}
			}
		} else {
			i+=BITS_PER_LONG;
			page += BITS_PER_LONG;
		}
	}
	total += count;

	/*
	 * Now free the allocator bitmap itself, it's not
	 * needed anymore:
	 */
	page = virt_to_page(bdata->node_bootmem_map);
	count = 0;
	for (i = 0; i < ((bdata->node_low_pfn-(bdata->node_boot_start >> PAGE_SHIFT))/8 + PAGE_SIZE-1)/PAGE_SIZE; i++,page++) {
		count++;
		__ClearPageReserved(page);
		set_page_count(page, 1);
		__free_page(page);
	}
	total += count;
	bdata->node_bootmem_map = NULL;

	return total;
}

unsigned long __init init_bootmem_node (pg_data_t *pgdat, unsigned long freepfn, unsigned long startpfn, unsigned long endpfn)
{
	return(init_bootmem_core(pgdat, freepfn, startpfn, endpfn));
}

void __init reserve_bootmem_node (pg_data_t *pgdat, unsigned long physaddr, unsigned long size)
{
	reserve_bootmem_core(pgdat->bdata, physaddr, size);
}

void __init free_bootmem_node (pg_data_t *pgdat, unsigned long physaddr, unsigned long size)
{
	free_bootmem_core(pgdat->bdata, physaddr, size);
}

unsigned long __init free_all_bootmem_node (pg_data_t *pgdat)
{
	return(free_all_bootmem_core(pgdat));
}

unsigned long __init init_bootmem (unsigned long start, unsigned long pages)
{
	max_low_pfn = pages;
	min_low_pfn = start;
	return(init_bootmem_core(NODE_DATA(0), start, 0, pages));
}

#ifndef CONFIG_HAVE_ARCH_BOOTMEM_NODE
void __init reserve_bootmem (unsigned long addr, unsigned long size)
{
	reserve_bootmem_core(NODE_DATA(0)->bdata, addr, size);
}
#endif /* !CONFIG_HAVE_ARCH_BOOTMEM_NODE */

void __init free_bootmem (unsigned long addr, unsigned long size)
{
	free_bootmem_core(NODE_DATA(0)->bdata, addr, size);
}

unsigned long __init free_all_bootmem (void)
{
	return(free_all_bootmem_core(NODE_DATA(0)));
}

void * __init __alloc_bootmem (unsigned long size, unsigned long align, unsigned long goal)
{
	pg_data_t *pgdat = pgdat_list;
	void *ptr;

	for_each_pgdat(pgdat)
		if ((ptr = __alloc_bootmem_core(pgdat->bdata, size,
						align, goal)))
			return(ptr);

	/*
	 * Whoops, we cannot satisfy the allocation request.
	 */
	printk(KERN_ALERT "bootmem alloc of %lu bytes failed!\n", size);
	panic("Out of memory");
	return NULL;
}

void * __init __alloc_bootmem_node (pg_data_t *pgdat, unsigned long size, unsigned long align, unsigned long goal)
{
	void *ptr;

	ptr = __alloc_bootmem_core(pgdat->bdata, size, align, goal);
	if (ptr)
		return (ptr);

	return __alloc_bootmem(size, align, goal);
}