[PATCH 5/5] btrfs: zoned: make auto-reclaim less aggressive

[Johannes Thumshirn <johannes.thumshirn@wdc.com>]

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>

---
Changes since v3:
* remove unusedd include (Filipe)
* Only call btrfs_zoned_should_reclaim() for zoned FSes (Josef)
* Use btrfs_calc_available_free_space() (Josef)

Changes since v2:
* Use div_u64()

Changes since RFC:
* Fix logic error
* Skip unavailable devices
* Use different metric working for non-zoned devices as well
---
 fs/btrfs/block-group.c | 10 ++++++++++
 fs/btrfs/zoned.c       | 23 +++++++++++++++++++++++
 fs/btrfs/zoned.h       |  6 ++++++
 3 files changed, 39 insertions(+)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 628741ecb97b..12454304bb85 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1512,6 +1512,13 @@ static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
 	return bg1->used > bg2->used;
 }
 
+static inline bool btrfs_should_reclaim(struct btrfs_fs_info *fs_info)
+{
+	if (btrfs_is_zoned(fs_info))
+		return btrfs_zoned_should_reclaim(fs_info);
+	return true;
+}
+
 void btrfs_reclaim_bgs_work(struct work_struct *work)
 {
 	struct btrfs_fs_info *fs_info =
@@ -1522,6 +1529,9 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
 		return;
 
+	if (!btrfs_should_reclaim(fs_info))
+		return;
+
 	sb_start_write(fs_info->sb);
 
 	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 1b1b310c3c51..f2a412427921 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -2079,3 +2079,26 @@ 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_space_info *sinfo;
+	u64 used = 0;
+	u64 total = 0;
+	u64 factor;
+
+	if (!btrfs_is_zoned(fs_info))
+		return false;
+
+	if (!fs_info->bg_reclaim_threshold)
+		return false;
+
+	list_for_each_entry(sinfo, &fs_info->space_info, list) {
+		total += sinfo->total_bytes;
+		used += btrfs_calc_available_free_space(fs_info, sinfo,
+							BTRFS_RESERVE_NO_FLUSH);
+	}
+
+	factor = div_u64(used * 100, total);
+	return factor >= fs_info->bg_reclaim_threshold;
+}
diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h
index c489c08d7fd5..f2d16395087f 100644
--- a/fs/btrfs/zoned.h
+++ b/fs/btrfs/zoned.h
@@ -74,6 +74,7 @@ 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)
@@ -232,6 +233,11 @@ 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)
-- 
2.35.1