btrfs: quasi-round-robin for chunk allocation

index 0ac712e..d8c9a49 100644
@@ -913,6 +913,31 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 	return 0;
 }
 
+/* Used to sort the devices by max_avail(descending sort) */
+int btrfs_cmp_device_free_bytes(const void *dev_info1, const void *dev_info2)
+{
+	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;
+}
+
+/*
+ * 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);
+}
+
 /*
  * The helper to calc the free space on the devices that can be used to store
  * file data.

index 8b9fb8c..a9f1fc2 100644
@@ -2282,19 +2282,6 @@ static noinline u64 chunk_bytes_by_type(u64 type, u64 calc_size,
 		return calc_size * num_stripes;
 }
 
-/* Used to sort the devices by max_avail(descending sort) */
-int btrfs_cmp_device_free_bytes(const void *dev_info1, const void *dev_info2)
-{
-	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;
-}
-
 static int __btrfs_calc_nstripes(struct btrfs_fs_devices *fs_devices, u64 type,
 				 int *num_stripes, int *min_stripes,
 				 int *sub_stripes)

index cc2eada..b502f01 100644
@@ -157,21 +157,6 @@ struct map_lookup {
 	struct btrfs_bio_stripe stripes[];
 };
 
-/* 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);
-}
-
 int btrfs_account_dev_extents_size(struct btrfs_device *device, u64 start,
 				   u64 end, u64 *length);
 

index a9f1fc2..45c592a 100644
@@ -849,10 +849,7 @@ int find_free_dev_extent(struct btrfs_trans_handle *trans,
 	/* we don't want to overwrite the superblock on the drive,
 	 * so we make sure to start at an offset of at least 1MB
 	 */
-	search_start = 1024 * 1024;
-
-	if (root->fs_info->alloc_start + num_bytes <= search_end)
-		search_start = max(root->fs_info->alloc_start, search_start);
+	search_start = max(root->fs_info->alloc_start, 1024ull * 1024);
 
 	max_hole_start = search_start;
 	max_hole_size = 0;

index 45c592a..77eb763 100644
@@ -2268,349 +2268,213 @@ static int btrfs_add_system_chunk(struct btrfs_trans_handle *trans,
 	return 0;
 }
 
-static noinline u64 chunk_bytes_by_type(u64 type, u64 calc_size,
-					int num_stripes, int sub_stripes)
-{
-	if (type & (BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_DUP))
-		return calc_size;
-	else if (type & BTRFS_BLOCK_GROUP_RAID10)
-		return calc_size * (num_stripes / sub_stripes);
-	else
-		return calc_size * num_stripes;
-}
-
-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;
-	}
-	if (type & (BTRFS_BLOCK_GROUP_DUP)) {
-		*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;
-	}
-	if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
-		*num_stripes = fs_devices->rw_devices;
-		if (*num_stripes < 4)
-			return -ENOSPC;
-		*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;
-	} else if (type & BTRFS_BLOCK_GROUP_METADATA) {
-		max_chunk_size = 256 * 1024 * 1024;
-		min_stripe_size = 32 * 1024 * 1024;
-	} else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
-		calc_size = 8 * 1024 * 1024;
-		max_chunk_size = calc_size * 2;
-		min_stripe_size = 1 * 1024 * 1024;
-	}
-
-	/* we don't want a chunk larger than 10% of writeable space */
-	max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
-			     max_chunk_size);
-
-	if (calc_size * num_stripes > max_chunk_size * ncopies) {
-		calc_size = max_chunk_size * ncopies;
-		do_div(calc_size, num_stripes);
-		do_div(calc_size, BTRFS_STRIPE_LEN);
-		calc_size *= BTRFS_STRIPE_LEN;
-	}
-
-	/* we don't want tiny stripes */
-	if (!small_stripe)
-		calc_size = max_t(u64, min_stripe_size, calc_size);
-
-	/*
-	 * 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, 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);
-
-	BUG_ON(map->num_stripes < num_stripes);
-
-	if (map->num_stripes == num_stripes)
-		return map;
-
-	new = kmalloc(len, GFP_NOFS);
-	if (!new) {
-		/* just change map->num_stripes */
-		map->num_stripes = num_stripes;
-		return map;
-	}
-
-	memcpy(new, map, len);
-	new->num_stripes = num_stripes;
-	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.
+ * sort the devices in descending order by max_avail, total_avail
  */
-static int __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_lookup,
-				    int min_stripes, u64 *stripe_size)
+static int btrfs_cmp_device_info(const void *a, const void *b)
 {
-	int i, index, sort_again = 0;
-	int min_devices = min_stripes;
-	u64 max_avail, min_free;
-	struct map_lookup *map = *map_lookup;
-	int ret;
-
-	if (nr_device < min_stripes)
-		return -ENOSPC;
-
-	btrfs_descending_sort_devices(devices, nr_device);
-
-	max_avail = devices[0].max_avail;
-	if (!max_avail)
-		return -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 (!devices[i].dev_offset) {
-			ret = find_free_dev_extent(trans, devices[i].dev,
-						   max_avail,
-						   &devices[i].dev_offset,
-						   &devices[i].max_avail);
-			if (ret != 0 && ret != -ENOSPC)
-				return ret;
-			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);
-
-	if (type & BTRFS_BLOCK_GROUP_DUP)
-		min_devices = 1;
-
-	if (!devices[min_devices - 1].max_avail)
-		return -ENOSPC;
-
-	max_avail = devices[min_devices - 1].max_avail;
-	if (type & BTRFS_BLOCK_GROUP_DUP)
-		do_div(max_avail, 2);
-
-	max_avail = __btrfs_calc_stripe_size(fs_devices, max_avail, type,
-					     min_stripes, 1);
-	if (type & BTRFS_BLOCK_GROUP_DUP)
-		min_free = max_avail * 2;
-	else
-		min_free = max_avail;
-
-	if (min_free > devices[min_devices - 1].max_avail)
-		return -ENOSPC;
-
-	map = __shrink_map_lookup_stripes(map, min_stripes);
-	*stripe_size = max_avail;
-
-	index = 0;
-	for (i = 0; i < min_stripes; i++) {
-		map->stripes[i].dev = devices[index].dev;
-		map->stripes[i].physical = devices[index].dev_offset;
-		if (type & BTRFS_BLOCK_GROUP_DUP) {
-			i++;
-			map->stripes[i].dev = devices[index].dev;
-			map->stripes[i].physical = devices[index].dev_offset +
-						   max_avail;
-		}
-		index++;
-	}
-	*map_lookup = map;
-
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+
+	if (di_a->max_avail > di_b->max_avail)
+		return -1;
+	if (di_a->max_avail < di_b->max_avail)
+		return 1;
+	if (di_a->total_avail > di_b->total_avail)
+		return -1;
+	if (di_a->total_avail < di_b->total_avail)
+		return 1;
 	return 0;
 }
 
 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 *num_bytes, u64 *stripe_size_out,
 			       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;
+	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;
+	struct btrfs_device_info *devices_info = NULL;
+	u64 total_avail;
+	u64 max_avail;
 	u64 dev_offset;
-	int num_stripes;
-	int min_stripes;
-	int sub_stripes;
-	int min_devices;	/* the min number of devices we need */
-	int i;
+	int num_stripes;	/* total number of stripes to allocate */
+	int sub_stripes;	/* sub_stripes info for map */
+	int dev_stripes;	/* stripes per dev */
+	int devs_max;		/* max devs to use */
+	int devs_min;		/* min devs needed */
+	int devs_increment;	/* ndevs has to be a multiple of this */
+	int ncopies;		/* how many copies to data has */
 	int ret;
+	u64 max_stripe_size;
+	u64 max_chunk_size;
+	u64 stripe_size;
+	int ndevs;
 	int index;
+	int i;
+	int j;
 
 	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;
+
+	sub_stripes = 1;
+	dev_stripes = 1;
+	devs_increment = 1;
+	ncopies = 1;
+	devs_max = 0;	/* 0 == as many as possible */
+	devs_min = 1;
+
+	/*
+	 * define the properties of each RAID type.
+	 * FIXME: move this to a global table and use it in all RAID
+	 * calculation code
+	 */
+	if (type & (BTRFS_BLOCK_GROUP_DUP)) {
+		dev_stripes = 2;
+		ncopies = 2;
+		devs_max = 1;
+	} else if (type & (BTRFS_BLOCK_GROUP_RAID0)) {
+		devs_min = 2;
+	} else if (type & (BTRFS_BLOCK_GROUP_RAID1)) {
+		devs_increment = 2;
+		ncopies = 2;
+		devs_max = 2;
+		devs_min = 2;
+	} else if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
+		sub_stripes = 2;
+		devs_increment = 2;
+		ncopies = 2;
+		devs_min = 4;
+	} else {
+		devs_max = 1;
+	}
+
+	if (type & BTRFS_BLOCK_GROUP_DATA) {
+		max_stripe_size = 1024 * 1024 * 1024;
+		max_chunk_size = 10 * max_stripe_size;
+	} else if (type & BTRFS_BLOCK_GROUP_METADATA) {
+		max_stripe_size = 256 * 1024 * 1024;
+		max_chunk_size = max_stripe_size;
+	} else if (type & BTRFS_BLOCK_GROUP_SYSTEM) {
+		max_stripe_size = 8 * 1024 * 1024;
+		max_chunk_size = 2 * max_stripe_size;
+	} else {
+		BUG_ON(1);
+	}
+
+	/* we don't want a chunk larger than 10% of writeable space */
+	max_chunk_size = min(div_factor(fs_devices->total_rw_bytes, 1),
+	                     max_chunk_size);
 
 	devices_info = kzalloc(sizeof(*devices_info) * fs_devices->rw_devices,
 			       GFP_NOFS);
 	if (!devices_info)
 		return -ENOMEM;
 
-	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;
-		min_devices = 1;
-	} else {
-		min_free = calc_size;
-		min_devices = min_stripes;
-	}
-
-	INIT_LIST_HEAD(&private_devs);
-	while (index < num_stripes) {
+	/*
+	 * in the first pass through the devices list, we gather information
+	 * about the available holes on each device.
+	 */
+	ndevs = 0;
+	while (cur != &fs_devices->alloc_list) {
 		device = list_entry(cur, struct btrfs_device, dev_alloc_list);
 		BUG_ON(!device->writeable);
+
+		cur = cur->next;
+
+		if (!device->in_fs_metadata)
+			continue;
+
 		if (device->total_bytes > device->bytes_used)
-			avail = device->total_bytes - device->bytes_used;
+			total_avail = device->total_bytes - device->bytes_used;
 		else
-			avail = 0;
-		cur = cur->next;
-
-		if (device->in_fs_metadata && avail >= min_free) {
-			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 =
-						devices_info[i].dev_offset;
-				index++;
-				if (type & BTRFS_BLOCK_GROUP_DUP) {
-					map->stripes[index].dev = device;
-					map->stripes[index].physical =
-						devices_info[i].dev_offset +
-						calc_size;
-					index++;
-				}
-			} else if (ret != -ENOSPC)
-				goto error;
-
-			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) {
-			num_stripes = index;
-			if (type & (BTRFS_BLOCK_GROUP_RAID10)) {
-				num_stripes /= sub_stripes;
-				num_stripes *= sub_stripes;
-			}
-
-			map = __shrink_map_lookup_stripes(map, num_stripes);
-		} else if (i >= min_devices) {
-			ret = __btrfs_alloc_tiny_space(trans, fs_devices,
-						       devices_info, i, type,
-						       &map, min_stripes,
-						       &calc_size);
-			if (ret)
-				goto error;
-		} else {
-			ret = -ENOSPC;
+			total_avail = 0;
+		/* avail is off by max(alloc_start, 1MB), but that is the same
+		 * for all devices, so it doesn't hurt the sorting later on
+		 */
+
+		ret = find_free_dev_extent(trans, device,
+		                           max_stripe_size * dev_stripes,
+					   &dev_offset, &max_avail);
+		if (ret && ret != -ENOSPC)
 			goto error;
+
+		if (ret == 0)
+			max_avail = max_stripe_size * dev_stripes;
+
+		if (max_avail < BTRFS_STRIPE_LEN * dev_stripes)
+			continue;
+
+		devices_info[ndevs].dev_offset = dev_offset;
+		devices_info[ndevs].max_avail = max_avail;
+		devices_info[ndevs].total_avail = total_avail;
+		devices_info[ndevs].dev = device;
+		++ndevs;
+	}
+
+	/*
+	 * now sort the devices by hole size / available space
+	 */
+	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
+	     btrfs_cmp_device_info, NULL);
+
+	/* round down to number of usable stripes */
+	ndevs -= ndevs % devs_increment;
+
+	if (ndevs < devs_increment * sub_stripes || ndevs < devs_min) {
+		ret = -ENOSPC;
+		goto error;
+	}
+
+	if (devs_max && ndevs > devs_max)
+		ndevs = devs_max;
+	/*
+	 * the primary goal is to maximize the number of stripes, so use as many
+	 * devices as possible, even if the stripes are not maximum sized.
+	 */
+	stripe_size = devices_info[ndevs-1].max_avail;
+	num_stripes = ndevs * dev_stripes;
+
+	if (stripe_size * num_stripes > max_chunk_size * ncopies) {
+		stripe_size = max_chunk_size * ncopies;
+		do_div(stripe_size, num_stripes);
+	}
+
+	do_div(stripe_size, dev_stripes);
+	do_div(stripe_size, BTRFS_STRIPE_LEN);
+	stripe_size *= BTRFS_STRIPE_LEN;
+
+	BUG_ON(!stripe_size);
+
+	map = kmalloc(map_lookup_size(num_stripes), GFP_NOFS);
+	if (!map) {
+		ret = -ENOMEM;
+		goto error;
+	}
+	map->num_stripes = num_stripes;
+
+	index = 0;
+	for (i = 0; i < ndevs; ++i) {
+		for (j = 0; j < dev_stripes; ++j) {
+			int s = i * dev_stripes + j;
+			map->stripes[s].dev = devices_info[i].dev;
+			map->stripes[s].physical = devices_info[i].dev_offset +
+                                                   j * stripe_size;
 		}
 	}
 	map->sector_size = extent_root->sectorsize;

@@ -2621,9 +2485,8 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	map->sub_stripes = sub_stripes;
 
 	*map_ret = map;
-	*stripe_size = calc_size;
-	*num_bytes = chunk_bytes_by_type(type, calc_size,
-					 map->num_stripes, sub_stripes);
+	*stripe_size_out = stripe_size;
+	*num_bytes = stripe_size * (num_stripes / ncopies);
 
 	trace_btrfs_chunk_alloc(info->chunk_root, map, start, *num_bytes);
 

@@ -2658,7 +2521,7 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 		ret = btrfs_alloc_dev_extent(trans, device,
 				info->chunk_root->root_key.objectid,
 				BTRFS_FIRST_CHUNK_TREE_OBJECTID,
-				start, dev_offset, calc_size);
+				start, dev_offset, stripe_size);
 		BUG_ON(ret);
 		index++;
 	}

@@ -2667,8 +2530,9 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	return 0;
 
 error:
+	kfree(devices_info);
 	kfree(map);
-	kfree(devices_info);
+
 	return ret;
 }
 

index b502f01..37ae6e2 100644
@@ -144,6 +144,7 @@ struct btrfs_device_info {
 	struct btrfs_device *dev;
 	u64 dev_offset;
 	u64 max_avail;
+	u64 total_avail;
 };
 
 struct map_lookup {