btrfs: zoned: make auto-reclaim less aggressive

The current auto-reclaim algorithm starts reclaiming all block-group's
with a zone_unusable value above a configured threshold. This is causing a
lot of reclaim IO even if there would be enough free zones on the device.

Instead of only accounting a block-group's zone_unusable value, also take
the number of empty zones into account.

Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

fs/btrfs/block-group.c

@@ -1522,6 +1522,9 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
 		return;
 
+	if (!btrfs_zoned_should_reclaim(fs_info))
+		return;
+
 	sb_start_write(fs_info->sb);
 
 	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {

fs/btrfs/zoned.c

@@ -15,6 +15,7 @@
 #include "transaction.h"
 #include "dev-replace.h"
 #include "space-info.h"
+#include "misc.h"
 
 /* Maximum number of zones to report per blkdev_report_zones() call */
 #define BTRFS_REPORT_NR_ZONES   4096
@@ -2078,3 +2079,32 @@ void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info)
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
 }
+
+bool btrfs_zoned_should_reclaim(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+	struct btrfs_device *device;
+	u64 bytes_used = 0;
+	u64 total_bytes = 0;
+	u64 factor;
+
+	if (!btrfs_is_zoned(fs_info))
+		return false;
+
+	if (!fs_info->bg_reclaim_threshold)
+		return false;
+
+	mutex_lock(&fs_devices->device_list_mutex);
+	list_for_each_entry(device, &fs_devices->devices, dev_list) {
+		if (!device->bdev)
+			continue;
+
+		total_bytes += device->disk_total_bytes;
+		bytes_used += device->bytes_used;
+
+	}
+	mutex_unlock(&fs_devices->device_list_mutex);
+
+	factor = (bytes_used * 100) / total_bytes;
+	return factor >= fs_info->bg_reclaim_threshold;
+}

fs/btrfs/zoned.h

@@ -78,6 +78,7 @@ void btrfs_zone_finish_endio(struct btrfs_fs_info *fs_info, u64 logical,
 			     u64 length);
 void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg);
 void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info);
+bool btrfs_zoned_should_reclaim(struct btrfs_fs_info *fs_info);
 #else /* CONFIG_BLK_DEV_ZONED */
 static inline int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
 				     struct blk_zone *zone)
@@ -236,6 +237,11 @@ static inline void btrfs_zone_finish_endio(struct btrfs_fs_info *fs_info,
 static inline void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg) { }
 
 static inline void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info) { }
+
+static inline bool btrfs_zoned_should_reclaim(struct btrfs_fs_info *fs_info)
+{
+	return false;
+}
 #endif
 
 static inline bool btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)