[PATCH 1/6] btrfs: report reclaim stats in sysfs

[Boris Burkov <boris@bur.io>]

When evaluating various reclaim strategies/thresholds against each
other, it is useful to collect data about the amount of reclaim
happening. Expose a count and byte count via sysfs per space_info.

Signed-off-by: Boris Burkov <boris@bur.io>
---
 fs/btrfs/block-group.c | 10 ++++++++++
 fs/btrfs/space-info.h  | 12 ++++++++++++
 fs/btrfs/sysfs.c       |  4 ++++
 3 files changed, 26 insertions(+)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 1e09aeea69c2..fd10e3b3f4f2 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1821,6 +1821,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	list_sort(NULL, &fs_info->reclaim_bgs, reclaim_bgs_cmp);
 	while (!list_empty(&fs_info->reclaim_bgs)) {
 		u64 zone_unusable;
+		u64 reclaimed;
 		int ret = 0;
 
 		bg = list_first_entry(&fs_info->reclaim_bgs,
@@ -1913,11 +1914,20 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 				div64_u64(bg->used * 100, bg->length),
 				div64_u64(zone_unusable * 100, bg->length));
 		trace_btrfs_reclaim_block_group(bg);
+		reclaimed = bg->used;
 		ret = btrfs_relocate_chunk(fs_info, bg->start);
 		if (ret) {
 			btrfs_dec_block_group_ro(bg);
 			btrfs_err(fs_info, "error relocating chunk %llu",
 				  bg->start);
+			spin_lock(&space_info->lock);
+			space_info->reclaim_count++;
+			spin_unlock(&space_info->lock);
+		} else {
+			spin_lock(&space_info->lock);
+			space_info->reclaim_count++;
+			space_info->reclaim_bytes += reclaimed;
+			spin_unlock(&space_info->lock);
 		}
 
 next:
diff --git a/fs/btrfs/space-info.h b/fs/btrfs/space-info.h
index a733458fd13b..b42db020eba6 100644
--- a/fs/btrfs/space-info.h
+++ b/fs/btrfs/space-info.h
@@ -165,6 +165,18 @@ struct btrfs_space_info {
 
 	struct kobject kobj;
 	struct kobject *block_group_kobjs[BTRFS_NR_RAID_TYPES];
+
+	/*
+	 * Monotonically increasing counter of block group reclaim attempts
+	 * Exposed in /sys/fs/<uuid>/allocation/<type>/reclaim_count
+	 */
+	u64 reclaim_count;
+
+	/*
+	 * Monotonically increasing counter of reclaimed bytes
+	 * Exposed in /sys/fs/<uuid>/allocation/<type>/reclaim_bytes
+	 */
+	u64 reclaim_bytes;
 };
 
 struct reserve_ticket {
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index c6387a8ddb94..0f3675c0f64f 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -894,6 +894,8 @@ SPACE_INFO_ATTR(bytes_readonly);
 SPACE_INFO_ATTR(bytes_zone_unusable);
 SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
+SPACE_INFO_ATTR(reclaim_count);
+SPACE_INFO_ATTR(reclaim_bytes);
 BTRFS_ATTR_RW(space_info, chunk_size, btrfs_chunk_size_show, btrfs_chunk_size_store);
 BTRFS_ATTR(space_info, size_classes, btrfs_size_classes_show);
 
@@ -949,6 +951,8 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, bg_reclaim_threshold),
 	BTRFS_ATTR_PTR(space_info, chunk_size),
 	BTRFS_ATTR_PTR(space_info, size_classes),
+	BTRFS_ATTR_PTR(space_info, reclaim_count),
+	BTRFS_ATTR_PTR(space_info, reclaim_bytes),
 #ifdef CONFIG_BTRFS_DEBUG
 	BTRFS_ATTR_PTR(space_info, force_chunk_alloc),
 #endif
-- 
2.44.0