btrfs: make the chunk allocator utilize the devices better

With this patch, we change the handling method when we can not get enough free
extents with default size.

Implementation:
1. Look up the suitable free extent on each device and keep the search result.
   If not find a suitable free extent, keep the max free extent
2. If we get enough suitable free extents with default size, chunk allocation
   succeeds.
3. If we can not get enough free extents, but the number of the extent with
   default size is >= min_stripes, we just change the mapping information
   (reduce the number of stripes in the extent map), and chunk allocation
   succeeds.
4. If the number of the extent with default size is < min_stripes, sort the
   devices by its max free extent's size descending
5. Use the size of the max free extent on the (num_stripes - 1)th device as the
   stripe size to allocate the device space

By this way, the chunk allocator can allocate chunks as large as possible when
the devices' space is not enough and make full use of the devices.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

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;
@@ -2256,51 +2253,209 @@ 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 > max_chunk_size * ncopies) {
 		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);
+
+	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.
+ */
+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)
+{
+	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);
 
-	do_div(calc_size, stripe_len);
-	calc_size *= stripe_len;
+	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;
+
+	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 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 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 min_devices;	/* the min number of devices we need */
+	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;
+
+	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;
 
-	if (type & BTRFS_BLOCK_GROUP_DUP)
+	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_devices = 1;
+	} 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;
+		min_devices = min_stripes;
+	}
 
 	INIT_LIST_HEAD(&private_devs);
 	while (index < num_stripes) {
@@ -2313,27 +2468,39 @@ 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;
+			} 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) {
@@ -2342,36 +2509,36 @@ 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)
-				do_div(calc_size, 2);
-			goto again;
+
+			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;
+			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;
 
 	*map_ret = map;
 	*stripe_size = calc_size;
 	*num_bytes = chunk_bytes_by_type(type, calc_size,
-					 num_stripes, sub_stripes);
+					 map->num_stripes, sub_stripes);
 
 	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 +2571,13 @@ 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,

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)))