diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 15e8c3f..c298367 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -877,7 +877,7 @@ out:
 	btrfs_free_path(path);
 error:
 	*start = max_hole_start;
-	if (len && max_hole_size > *len)
+	if (len)
 		*len = max_hole_size;
 	return ret;
 }
@@ -2176,70 +2176,67 @@ static noinline u64 chunk_bytes_by_type(u64 type, u64 calc_size,
 		return calc_size * num_stripes;
 }
 
-static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
-			       struct btrfs_root *extent_root,
-			       struct map_lookup **map_ret,
-			       u64 *num_bytes, u64 *stripe_size,
-			       u64 start, u64 type)
+/* Used to sort the devices by max_avail(descending sort) */
+int btrfs_cmp_device_free_bytes(const void *dev_info1, const void *dev_info2)
 {
-	struct btrfs_fs_info *info = extent_root->fs_info;
-	struct btrfs_device *device = NULL;
-	struct btrfs_fs_devices *fs_devices = info->fs_devices;
-	struct list_head *cur;
-	struct map_lookup *map = NULL;
-	struct extent_map_tree *em_tree;
-	struct extent_map *em;
-	struct list_head private_devs;
-	int min_stripe_size = 1 * 1024 * 1024;
-	u64 calc_size = 1024 * 1024 * 1024;
-	u64 max_chunk_size = calc_size;
-	u64 min_free;
-	u64 avail;
-	u64 max_avail = 0;
-	u64 dev_offset;
-	int num_stripes = 1;
-	int min_stripes = 1;
-	int sub_stripes = 0;
-	int ncopies = 1;
-	int looped = 0;
-	int ret;
-	int index;
-	int stripe_len = 64 * 1024;
+	if (((struct btrfs_device_info *)dev_info1)->max_avail >
+	    ((struct btrfs_device_info *)dev_info2)->max_avail)
+		return -1;
+	else if (((struct btrfs_device_info *)dev_info1)->max_avail <
+		 ((struct btrfs_device_info *)dev_info2)->max_avail)
+		return 1;
+	else
+		return 0;
+}
 
-	if ((type & BTRFS_BLOCK_GROUP_RAID1) &&
-	    (type & BTRFS_BLOCK_GROUP_DUP)) {
-		WARN_ON(1);
-		type &= ~BTRFS_BLOCK_GROUP_DUP;
-	}
-	if (list_empty(&fs_devices->alloc_list))
-		return -ENOSPC;
+static int __btrfs_calc_nstripes(struct btrfs_fs_devices *fs_devices, u64 type,
+				 int *num_stripes, int *min_stripes,
+				 int *sub_stripes)
+{
+	*num_stripes = 1;
+	*min_stripes = 1;
+	*sub_stripes = 0;
 
 	if (type & (BTRFS_BLOCK_GROUP_RAID0)) {
-		num_stripes = fs_devices->rw_devices;
-		min_stripes = 2;
+		*num_stripes = fs_devices->rw_devices;
+		*min_stripes = 2;
 	}
 	if (type & (BTRFS_BLOCK_GROUP_DUP)) {
-		num_stripes = 2;
-		min_stripes = 2;
-		ncopies = 2;
+		*num_stripes = 2;
+		*min_stripes = 2;
 	}
 	if (type & (BTRFS_BLOCK_GROUP_RAID1)) {
 		if (fs_devices->rw_devices < 2)
 			return -ENOSPC;
-		num_stripes = 2;
-		min_stripes = 2;
-		ncopies = 2;
+		*num_stripes = 2;
+		*min_stripes = 2;
 	}
 	if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
-		num_stripes = fs_devices->rw_devices;
-		if (num_stripes < 4)
+		*num_stripes = fs_devices->rw_devices;
+		if (*num_stripes < 4)
 			return -ENOSPC;
-		num_stripes &= ~(u32)1;
-		sub_stripes = 2;
-		ncopies = 2;
-		min_stripes = 4;
+		*num_stripes &= ~(u32)1;
+		*sub_stripes = 2;
+		*min_stripes = 4;
 	}
 
+	return 0;
+}
+
+static u64 __btrfs_calc_stripe_size(struct btrfs_fs_devices *fs_devices,
+				    u64 proposed_size, u64 type,
+				    int num_stripes, int small_stripe)
+{
+	int min_stripe_size = 1 * 1024 * 1024;
+	u64 calc_size = proposed_size;
+	u64 max_chunk_size = calc_size;
+	int ncopies = 1;
+
+	if (type & (BTRFS_BLOCK_GROUP_RAID1 |
+		    BTRFS_BLOCK_GROUP_DUP |
+		    BTRFS_BLOCK_GROUP_RAID10))
+		ncopies = 2;
+
 	if (type & BTRFS_BLOCK_GROUP_DATA) {
 		max_chunk_size = 10 * calc_size;
 		min_stripe_size = 64 * 1024 * 1024;
@@ -2256,52 +2253,211 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
 			     max_chunk_size);
 
-again:
-	max_avail = 0;
-	if (!map || map->num_stripes != num_stripes) {
-		kfree(map);
-		map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
-		if (!map)
-			return -ENOMEM;
-		map->num_stripes = num_stripes;
-	}
-
 	if (calc_size * num_stripes / ncopies > max_chunk_size) {
 		calc_size = max_chunk_size * ncopies;
 		do_div(calc_size, num_stripes);
-		do_div(calc_size, stripe_len);
-		calc_size *= stripe_len;
+		do_div(calc_size, BTRFS_STRIPE_LEN);
+		calc_size *= BTRFS_STRIPE_LEN;
 	}
 
 	/* we don't want tiny stripes */
-	if (!looped)
+	if (!small_stripe)
 		calc_size = max_t(u64, min_stripe_size, calc_size);
 
 	/*
-	 * we're about to do_div by the stripe_len so lets make sure
+	 * we're about to do_div by the BTRFS_STRIPE_LEN so lets make sure
 	 * we end up with something bigger than a stripe
 	 */
-	calc_size = max_t(u64, calc_size, stripe_len * 4);
+	calc_size = max_t(u64, calc_size, BTRFS_STRIPE_LEN);
+
+	do_div(calc_size, BTRFS_STRIPE_LEN);
+	calc_size *= BTRFS_STRIPE_LEN;
+
+	return calc_size;
+}
+
+static struct map_lookup *__shrink_map_lookup_stripes(struct map_lookup *map,
+						      int num_stripes)
+{
+	struct map_lookup *new;
+	size_t len = map_lookup_size(num_stripes);
+
+	new = kmalloc(len, GFP_NOFS);
+	if (!new) {
+		/* just change map->num_stripes */
+		map->num_stripes = num_stripes;
+		return map;
+	}
+
+	memcpy(new, map, len);
+	kfree(map);
+	return new;
+}
+
+/*
+ * helper to allocate device space from btrfs_device_info, in which we stored
+ * max free space information of every device. It is used when we can not
+ * allocate chunks by default size.
+ *
+ * By this helper, we can allocate a new chunk as larger as possible.
+ */
+static struct map_lookup *__btrfs_alloc_tiny_space(
+					struct btrfs_trans_handle *trans,
+					struct btrfs_fs_devices *fs_devices,
+					struct btrfs_device_info *devices,
+					int nr_device, u64 type,
+					struct map_lookup *map,
+					int num_stripes, int min_stripes,
+					u64 *stripe_size)
+{
+	int i, sort_again = 0;
+	u64 max_avail, min_free;
+
+	if (nr_device < min_stripes)
+		return ERR_PTR(-ENOSPC);
+
+	if (nr_device < num_stripes)
+		num_stripes = nr_device;
+
+	btrfs_descending_sort_devices(devices, nr_device);
+
+	max_avail = devices[0].max_avail;
+	if (!max_avail)
+		return ERR_PTR(-ENOSPC);
+
+	for (i = 0; i < nr_device; i++) {
+		/*
+		 * if dev_offset = 0, it means the free space of this device
+		 * is less than what we need, and we didn't search max avail
+		 * extent on this device, so do it now.
+		 *
+		 * if max_avail = 0, it means when we search max avail extent
+		 * on this device, error happened, so try to search again.
+		 */
+		if (!devices[i].dev_offset || !devices[i].max_avail) {
+			find_free_dev_extent(trans, devices[i].dev, max_avail,
+					     &devices[i].dev_offset,
+					     &devices[i].max_avail);
+			sort_again = 1;
+		}
+	}
+
+	/* we update the max avail free extent of each devices, sort again */
+	if (sort_again)
+		btrfs_descending_sort_devices(devices, nr_device);
+
+	i = num_stripes - 1;
+	for (; i >= min_stripes - 1; i--) {
+		if (!devices[i].max_avail) {
+			num_stripes--;
+			continue;
+		}
 
-	do_div(calc_size, stripe_len);
-	calc_size *= stripe_len;
+		BUG_ON(!devices[i].dev_offset);
+
+		max_avail = devices[i].max_avail;
+		if (type & BTRFS_BLOCK_GROUP_DUP)
+			max_avail /= 2;
+
+		max_avail = __btrfs_calc_stripe_size(fs_devices, max_avail,
+						     type, num_stripes, 1);
+		if (type & BTRFS_BLOCK_GROUP_DUP)
+			min_free = max_avail * 2;
+		else
+			min_free = max_avail;
+
+		if (min_free <= devices[i].max_avail)
+			break;
+
+		num_stripes--;
+	}
+
+	if (i < min_stripes - 1)
+		return ERR_PTR(-ENOSPC);
+
+	num_stripes = i + 1;
+	map = __shrink_map_lookup_stripes(map, num_stripes);
+	*stripe_size = max_avail;
+
+	for (i = 0; i < num_stripes; i++) {
+		map->stripes[i].dev = devices[i].dev;
+		map->stripes[i].physical = devices[i].dev_offset;
+		if (type & BTRFS_BLOCK_GROUP_DUP) {
+			map->stripes[i].dev = devices[i].dev;
+			map->stripes[i].physical = devices[i].dev_offset +
+						   max_avail;
+		}
+	}
+
+	return map;
+}
+
+static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *extent_root,
+			       struct map_lookup **map_ret,
+			       u64 *num_bytes, u64 *stripe_size,
+			       u64 start, u64 type)
+{
+	struct btrfs_fs_info *info = extent_root->fs_info;
+	struct btrfs_device *device = NULL;
+	struct btrfs_fs_devices *fs_devices = info->fs_devices;
+	struct list_head *cur;
+	struct map_lookup *map = NULL;
+	struct extent_map_tree *em_tree;
+	struct extent_map *em;
+	struct btrfs_device_info *devices_info;
+	struct list_head private_devs;
+	u64 calc_size = 1024 * 1024 * 1024;
+	u64 min_free;
+	u64 avail;
+	u64 dev_offset;
+	int num_stripes;
+	int min_stripes;
+	int sub_stripes;
+	int i;
+	int ret;
+	int index;
+
+	if ((type & BTRFS_BLOCK_GROUP_RAID1) &&
+	    (type & BTRFS_BLOCK_GROUP_DUP)) {
+		WARN_ON(1);
+		type &= ~BTRFS_BLOCK_GROUP_DUP;
+	}
+	if (list_empty(&fs_devices->alloc_list))
+		return -ENOSPC;
+
+	ret = __btrfs_calc_nstripes(fs_devices, type, &num_stripes,
+				    &min_stripes, &sub_stripes);
+	if (ret)
+		return ret;
+
+	devices_info = kzalloc(sizeof(*devices_info) * fs_devices->rw_devices,
+			       GFP_NOFS);
+	if (!devices_info)
+		return -ENOMEM;
+
+	if (!map || map->num_stripes != num_stripes) {
+		kfree(map);
+		map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
+		if (!map) {
+			ret = -ENOMEM;
+			goto error;
+		}
+		map->num_stripes = num_stripes;
+	}
 
 	cur = fs_devices->alloc_list.next;
 	index = 0;
+	i = 0;
+
+	calc_size = __btrfs_calc_stripe_size(fs_devices, calc_size, type,
+					     num_stripes, 0);
 
 	if (type & BTRFS_BLOCK_GROUP_DUP)
 		min_free = calc_size * 2;
 	else
 		min_free = calc_size;
 
-	/*
-	 * we add 1MB because we never use the first 1MB of the device, unless
-	 * we've looped, then we are likely allocating the maximum amount of
-	 * space left already
-	 */
-	if (!looped)
-		min_free += 1024 * 1024;
-
 	INIT_LIST_HEAD(&private_devs);
 	while (index < num_stripes) {
 		device = list_entry(cur, struct btrfs_device, dev_alloc_list);
@@ -2313,27 +2469,37 @@ again:
 		cur = cur->next;
 
 		if (device->in_fs_metadata && avail >= min_free) {
-			ret = find_free_dev_extent(trans, device,
-						   min_free, &dev_offset,
-						   &max_avail);
+			ret = find_free_dev_extent(trans, device, min_free,
+						   &devices_info[i].dev_offset,
+						   &devices_info[i].max_avail);
 			if (ret == 0) {
 				list_move_tail(&device->dev_alloc_list,
 					       &private_devs);
 				map->stripes[index].dev = device;
-				map->stripes[index].physical = dev_offset;
+				map->stripes[index].physical =
+						devices_info[i].dev_offset;
 				index++;
 				if (type & BTRFS_BLOCK_GROUP_DUP) {
 					map->stripes[index].dev = device;
 					map->stripes[index].physical =
-						dev_offset + calc_size;
+						devices_info[i].dev_offset +
+						calc_size;
 					index++;
 				}
 			}
-		} else if (device->in_fs_metadata && avail > max_avail)
-			max_avail = avail;
+			devices_info[i].dev = device;
+			i++;
+		} else if (device->in_fs_metadata &&
+			   avail >= BTRFS_STRIPE_LEN) {
+			devices_info[i].dev = device;
+			devices_info[i].max_avail = avail;
+			i++;
+		}
+
 		if (cur == &fs_devices->alloc_list)
 			break;
 	}
+
 	list_splice(&private_devs, &fs_devices->alloc_list);
 	if (index < num_stripes) {
 		if (index >= min_stripes) {
@@ -2342,23 +2508,26 @@ again:
 				num_stripes /= sub_stripes;
 				num_stripes *= sub_stripes;
 			}
-			looped = 1;
-			goto again;
-		}
-		if (!looped && max_avail > 0) {
-			looped = 1;
-			calc_size = max_avail;
-			if (type & BTRFS_BLOCK_GROUP_DUP)
-				calc_size /= 2;
-			goto again;
+
+			map = __shrink_map_lookup_stripes(map, num_stripes);
+		} else if (i >= min_stripes) {
+			map = __btrfs_alloc_tiny_space(trans, fs_devices,
+						       devices_info, i, type,
+						       map, num_stripes,
+						       min_stripes, &calc_size);
+			if (IS_ERR(map)) {
+				ret = PTR_ERR(map);
+				goto error;
+			}
+		} else {
+			ret = -ENOSPC;
+			goto error;
 		}
-		kfree(map);
-		return -ENOSPC;
 	}
 	map->sector_size = extent_root->sectorsize;
-	map->stripe_len = stripe_len;
-	map->io_align = stripe_len;
-	map->io_width = stripe_len;
+	map->stripe_len = BTRFS_STRIPE_LEN;
+	map->io_align = BTRFS_STRIPE_LEN;
+	map->io_width = BTRFS_STRIPE_LEN;
 	map->type = type;
 	map->num_stripes = num_stripes;
 	map->sub_stripes = sub_stripes;
@@ -2370,8 +2539,8 @@ again:
 
 	em = alloc_extent_map(GFP_NOFS);
 	if (!em) {
-		kfree(map);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto error;
 	}
 	em->bdev = (struct block_device *)map;
 	em->start = start;
@@ -2404,7 +2573,13 @@ again:
 		index++;
 	}
 
+	kfree(devices_info);
 	return 0;
+
+error:
+	kfree(map);
+	kfree(devices_info);
+	return ret;
 }
 
 static int __finish_chunk_alloc(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index a668c01..a5cfedf 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -20,8 +20,11 @@
 #define __BTRFS_VOLUMES_
 
 #include <linux/bio.h>
+#include <linux/sort.h>
 #include "async-thread.h"
 
+#define BTRFS_STRIPE_LEN	(64 * 1024)
+
 struct buffer_head;
 struct btrfs_pending_bios {
 	struct bio *head;
@@ -137,6 +140,27 @@ struct btrfs_multi_bio {
 	struct btrfs_bio_stripe stripes[];
 };
 
+struct btrfs_device_info {
+	struct btrfs_device *dev;
+	u64 dev_offset;
+	u64 max_avail;
+};
+
+/* Used to sort the devices by max_avail(descending sort) */
+int btrfs_cmp_device_free_bytes(const void *dev_info1, const void *dev_info2);
+
+/*
+ * sort the devices by max_avail, in which max free extent size of each device
+ * is stored.(Descending Sort)
+ */
+static inline void btrfs_descending_sort_devices(
+					struct btrfs_device_info *devices,
+					size_t nr_devices)
+{
+	sort(devices, nr_devices, sizeof(struct btrfs_device_info),
+	     btrfs_cmp_device_free_bytes, NULL);
+}
+
 #define btrfs_multi_bio_size(n) (sizeof(struct btrfs_multi_bio) + \
 			    (sizeof(struct btrfs_bio_stripe) * (n)))
 
