btrfs: factor out decide_stripe_size()

Factor out decide_stripe_size() from __btrfs_alloc_chunk(). This
function calculates the actual stripe size to allocate.
decide_stripe_size() handles the common case to round down the 'ndevs'
to 'devs_increment' and check the upper and lower limitation of 'ndevs'.
decide_stripe_size_regular() decides the size of a stripe and the size
of a chunk. The policy is to maximize the number of stripes.

This commit has no functional changes.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -4943,6 +4943,82 @@ static int gather_device_info(struct btrfs_fs_devices *fs_devices,
 	return 0;
 }
 
+static int decide_stripe_size_regular(struct alloc_chunk_ctl *ctl,
+				      struct btrfs_device_info *devices_info)
+{
+	/* Number of stripes that count for block group size */
+	int data_stripes;
+
+	/*
+	 * 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.
+	 *
+	 * The DUP profile stores more than one stripe per device, the
+	 * max_avail is the total size so we have to adjust.
+	 */
+	ctl->stripe_size = div_u64(devices_info[ctl->ndevs - 1].max_avail,
+				   ctl->dev_stripes);
+	ctl->num_stripes = ctl->ndevs * ctl->dev_stripes;
+
+	/* This will have to be fixed for RAID1 and RAID10 over more drives */
+	data_stripes = (ctl->num_stripes - ctl->nparity) / ctl->ncopies;
+
+	/*
+	 * Use the number of data stripes to figure out how big this chunk is
+	 * really going to be in terms of logical address space, and compare
+	 * that answer with the max chunk size. If it's higher, we try to
+	 * reduce stripe_size.
+	 */
+	if (ctl->stripe_size * data_stripes > ctl->max_chunk_size) {
+		/*
+		 * Reduce stripe_size, round it up to a 16MB boundary again and
+		 * then use it, unless it ends up being even bigger than the
+		 * previous value we had already.
+		 */
+		ctl->stripe_size = min(round_up(div_u64(ctl->max_chunk_size,
+							data_stripes), SZ_16M),
+				       ctl->stripe_size);
+	}
+
+	/* Align to BTRFS_STRIPE_LEN */
+	ctl->stripe_size = round_down(ctl->stripe_size, BTRFS_STRIPE_LEN);
+	ctl->chunk_size = ctl->stripe_size * data_stripes;
+
+	return 0;
+}
+
+static int decide_stripe_size(struct btrfs_fs_devices *fs_devices,
+			      struct alloc_chunk_ctl *ctl,
+			      struct btrfs_device_info *devices_info)
+{
+	struct btrfs_fs_info *info = fs_devices->fs_info;
+
+	/*
+	 * Round down to number of usable stripes, devs_increment can be any
+	 * number so we can't use round_down() that requires power of 2, while
+	 * rounddown is safe.
+	 */
+	ctl->ndevs = rounddown(ctl->ndevs, ctl->devs_increment);
+
+	if (ctl->ndevs < ctl->devs_min) {
+		if (btrfs_test_opt(info, ENOSPC_DEBUG)) {
+			btrfs_debug(info,
+	"%s: not enough devices with free space: have=%d minimum required=%d",
+				    __func__, ctl->ndevs, ctl->devs_min);
+		}
+		return -ENOSPC;
+	}
+
+	ctl->ndevs = min(ctl->ndevs, ctl->devs_max);
+
+	switch (fs_devices->chunk_alloc_policy) {
+	case BTRFS_CHUNK_ALLOC_REGULAR:
+		return decide_stripe_size_regular(ctl, devices_info);
+	default:
+		BUG();
+	}
+}
+
 static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 			       u64 start, u64 type)
 {
@@ -4953,8 +5029,6 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	struct extent_map *em;
 	struct btrfs_device_info *devices_info = NULL;
 	struct alloc_chunk_ctl ctl;
-	/* Number of stripes that count for block group size */
-	int data_stripes;
 	int ret;
 	int i;
 	int j;
@@ -4989,61 +5063,9 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	if (ret < 0)
 		goto error;
 
-	/*
-	 * Round down to number of usable stripes, devs_increment can be any
-	 * number so we can't use round_down()
-	 */
-	ctl.ndevs -= ctl.ndevs % ctl.devs_increment;
-
-	if (ctl.ndevs < ctl.devs_min) {
-		ret = -ENOSPC;
-		if (btrfs_test_opt(info, ENOSPC_DEBUG)) {
-			btrfs_debug(info,
-	"%s: not enough devices with free space: have=%d minimum required=%d",
-				    __func__, ctl.ndevs, ctl.devs_min);
-		}
+	ret = decide_stripe_size(fs_devices, &ctl, devices_info);
+	if (ret < 0)
 		goto error;
-	}
-
-	ctl.ndevs = min(ctl.ndevs, ctl.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.
-	 *
-	 * The DUP profile stores more than one stripe per device, the
-	 * max_avail is the total size so we have to adjust.
-	 */
-	ctl.stripe_size = div_u64(devices_info[ctl.ndevs - 1].max_avail,
-				   ctl.dev_stripes);
-	ctl.num_stripes = ctl.ndevs * ctl.dev_stripes;
-
-	/*
-	 * this will have to be fixed for RAID1 and RAID10 over
-	 * more drives
-	 */
-	data_stripes = (ctl.num_stripes - ctl.nparity) / ctl.ncopies;
-
-	/*
-	 * Use the number of data stripes to figure out how big this chunk
-	 * is really going to be in terms of logical address space,
-	 * and compare that answer with the max chunk size. If it's higher,
-	 * we try to reduce stripe_size.
-	 */
-	if (ctl.stripe_size * data_stripes > ctl.max_chunk_size) {
-		/*
-		 * Reduce stripe_size, round it up to a 16MB boundary again and
-		 * then use it, unless it ends up being even bigger than the
-		 * previous value we had already.
-		 */
-		ctl.stripe_size =
-			min(round_up(div_u64(ctl.max_chunk_size, data_stripes),
-				     SZ_16M),
-			    ctl.stripe_size);
-	}
-
-	/* align to BTRFS_STRIPE_LEN */
-	ctl.stripe_size = round_down(ctl.stripe_size, BTRFS_STRIPE_LEN);
 
 	map = kmalloc(map_lookup_size(ctl.num_stripes), GFP_NOFS);
 	if (!map) {
@@ -5067,8 +5089,6 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	map->type = type;
 	map->sub_stripes = ctl.sub_stripes;
 
-	ctl.chunk_size = ctl.stripe_size * data_stripes;
-
 	trace_btrfs_chunk_alloc(info, map, start, ctl.chunk_size);
 
 	em = alloc_extent_map();