This is helpful to look fragmentation. This is an test code to look size of zeros.
Test result is '10+9+994=>1013 found of total: 1024'

unsigned long search_idx, found_idx, nr_found_tot;
unsigned long bitmap_max;
unsigned int nr_found;
unsigned long *bitmap;

search_idx = nr_found_tot = 0;
bitmap_max = 1024;
bitmap = kzalloc(BITS_TO_LONGS(bitmap_max) * sizeof(long),
		 GFP_KERNEL);

/* test bitmap_set offset, count */
bitmap_set(bitmap, 10, 1);
bitmap_set(bitmap, 20, 10);

for (;;) {
	found_idx = bitmap_find_next_zero_area_and_size(bitmap,
				bitmap_max, search_idx, &nr_found);
	if (found_idx >= bitmap_max)
		break;
	if (nr_found_tot == 0)
		printk("%u", nr_found);
	else
		printk("+%u", nr_found);
	nr_found_tot += nr_found;
	search_idx = found_idx + nr_found;
}
printk("=>%lu found of total: %lu\n", nr_found_tot, bitmap_max);

Signed-off-by: Jaewon Kim <redacted>
---
 include/linux/bitmap.h |  6 ++++++
 lib/bitmap.c           | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 3b77588..b724a6c 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h

@@ -46,6 +46,7 @@
  * bitmap_clear(dst, pos, nbits)		Clear specified bit area
  * bitmap_find_next_zero_area(buf, len, pos, n, mask)	Find bit free area
  * bitmap_find_next_zero_area_off(buf, len, pos, n, mask)	as above
+ * bitmap_find_next_zero_area_and_size(buf, len, pos, n, mask)	Find bit free area and its size
  * bitmap_shift_right(dst, src, n, nbits)	*dst = *src >> n
  * bitmap_shift_left(dst, src, n, nbits)	*dst = *src << n
  * bitmap_remap(dst, src, old, new, nbits)	*dst = map(old, new)(src)

@@ -123,6 +124,11 @@ extern unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 						    unsigned long align_mask,
 						    unsigned long align_offset);
 
+extern unsigned long bitmap_find_next_zero_area_and_size(unsigned long *map,
+							 unsigned long size,
+							 unsigned long start,
+							 unsigned int *nr);
+
 /**
  * bitmap_find_next_zero_area - find a contiguous aligned zero area
  * @map: The address to base the search on

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 0b66f0e..d02817c 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c

@@ -332,6 +332,31 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 }
 EXPORT_SYMBOL(bitmap_find_next_zero_area_off);
 
+/**
+ * bitmap_find_next_zero_area_and_size - find a contiguous aligned zero area
+ * @map: The address to base the search on
+ * @size: The bitmap size in bits
+ * @start: The bitnumber to start searching at
+ * @nr: The number of zeroed bits we've found
+ */
+unsigned long bitmap_find_next_zero_area_and_size(unsigned long *map,
+					     unsigned long size,
+					     unsigned long start,
+					     unsigned int *nr)
+{
+	unsigned long index, i;
+
+	*nr = 0;
+	index = find_next_zero_bit(map, size, start);
+
+	if (index >= size)
+		return index;
+	i = find_next_bit(map, size, index);
+	*nr = i - index;
+	return index;
+}
+EXPORT_SYMBOL(bitmap_find_next_zero_area_and_size);
+
 /*
  * Bitmap printing & parsing functions: first version by Nadia Yvette Chambers,
  * second version by Paul Jackson, third by Joe Korty.

-- 
1.9.1