[PATCH 2/2] btrfs: create chunk device type aware

[Anand Jain <anand.jain@oracle.com>]

Mixed device types configuration exist. Most commonly, HDD mixed with
SSD/NVME device types. This use case prefers that the data chunk
allocates on HDD and the metadata chunk allocates on the SSD/NVME.

As of now, in the function gather_device_info() called from
btrfs_create_chunk(), we sort the devices based on unallocated space
only.

After this patch, this function will check for mixed device types. And
will sort the devices based on enum btrfs_device_types. That is, sort if
the allocation type is metadata and reverse-sort if the allocation type
is data.

The advantage of this method is that data/metadata allocation distribution
based on the device type happens automatically without any manual
configuration.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/volumes.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index da3d6d0f5bc3..77fba78555d7 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5060,6 +5060,37 @@ static int btrfs_add_system_chunk(struct btrfs_fs_info *fs_info,
 	return 0;
 }
 
+/*
+ * Sort the devices in its ascending order of latency value.
+ */
+static int btrfs_cmp_device_latency(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+	struct btrfs_device *dev_a = di_a->dev;
+	struct btrfs_device *dev_b = di_b->dev;
+
+	if (dev_a->dev_type > dev_b->dev_type)
+		return 1;
+	if (dev_a->dev_type < dev_b->dev_type)
+		return -1;
+	return 0;
+}
+
+static int btrfs_cmp_device_rev_latency(const void *a, const void *b)
+{
+	const struct btrfs_device_info *di_a = a;
+	const struct btrfs_device_info *di_b = b;
+	struct btrfs_device *dev_a = di_a->dev;
+	struct btrfs_device *dev_b = di_b->dev;
+
+	if (dev_a->dev_type > dev_b->dev_type)
+		return -1;
+	if (dev_a->dev_type < dev_b->dev_type)
+		return 1;
+	return 0;
+}
+
 /*
  * sort the devices in descending order by max_avail, total_avail
  */
@@ -5292,6 +5323,20 @@ static int gather_device_info(struct btrfs_fs_devices *fs_devices,
 	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
 	     btrfs_cmp_device_info, NULL);
 
+	/*
+	 * Sort devices by their latency. Ascending order of latency for
+	 * metadata and descending order of latency for the data chunks for
+	 * mixed device types.
+	 */
+	if (fs_devices->mixed_dev_types) {
+		if (ctl->type & BTRFS_BLOCK_GROUP_DATA)
+			sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
+			     btrfs_cmp_device_rev_latency, NULL);
+		else
+			sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
+			     btrfs_cmp_device_latency, NULL);
+	}
+
 	return 0;
 }
 
-- 
2.33.1