[PATCH v2 2/7] btrfs: use u8 for reclaim threshold type

[Sun YangKai <sunk67188@gmail.com>]

The bg_reclaim_threshold field stores a percentage value (0-100), making
u8 a more appropriate type than int. Update the field and related
function return types:

- struct btrfs_space_info::bg_reclaim_threshold
- calc_dynamic_reclaim_threshold()
- btrfs_calc_reclaim_threshold()

The sysfs store function already validates the range is 0-100, ensuring
the cast to u8 is safe.

Signed-off-by: Sun YangKai <sunk67188@gmail.com>
---
 fs/btrfs/space-info.c |  6 +++---
 fs/btrfs/space-info.h | 14 +++++++-------
 fs/btrfs/sysfs.c      |  3 ++-
 3 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index de8bde1081be..29dffbd9aadd 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -2037,7 +2037,7 @@ static u64 calc_unalloc_target(struct btrfs_fs_info *fs_info)
  * Typically with 10 block groups as the target, the discrete values this comes
  * out to are 0, 10, 20, ... , 80, 90, and 99.
  */
-static int calc_dynamic_reclaim_threshold(const struct btrfs_space_info *space_info)
+static u8 calc_dynamic_reclaim_threshold(const struct btrfs_space_info *space_info)
 {
 	struct btrfs_fs_info *fs_info = space_info->fs_info;
 	u64 unalloc = atomic64_read(&fs_info->free_chunk_space);
@@ -2052,11 +2052,11 @@ static int calc_dynamic_reclaim_threshold(const struct btrfs_space_info *space_i
 	if (unused < data_chunk_size)
 		return 0;
 
-	/* Cast to int is OK because want <= target. */
+	/* Cast to u8 is OK because want <= target. */
 	return calc_pct_ratio(want, target);
 }
 
-int btrfs_calc_reclaim_threshold(const struct btrfs_space_info *space_info)
+u8 btrfs_calc_reclaim_threshold(const struct btrfs_space_info *space_info)
 {
 	lockdep_assert_held(&space_info->lock);
 
diff --git a/fs/btrfs/space-info.h b/fs/btrfs/space-info.h
index a49a4c7b0a68..3cf22d7fad20 100644
--- a/fs/btrfs/space-info.h
+++ b/fs/btrfs/space-info.h
@@ -132,15 +132,15 @@ struct btrfs_space_info {
 	/* Chunk size in bytes */
 	u64 chunk_size;
 
+	int clamp;		/* Used to scale our threshold for preemptive
+				   flushing. The value is >> clamp, so turns
+				   out to be a 2^clamp divisor. */
+
 	/*
 	 * Once a block group drops below this threshold (percents) we'll
 	 * schedule it for reclaim.
 	 */
-	int bg_reclaim_threshold;
-
-	int clamp;		/* Used to scale our threshold for preemptive
-				   flushing. The value is >> clamp, so turns
-				   out to be a 2^clamp divisor. */
+	u8 bg_reclaim_threshold;
 
 	bool full;		/* indicates that we cannot allocate any more
 				   chunks for this space */
@@ -217,7 +217,7 @@ struct btrfs_space_info {
 	 * freed any space since the last time we made no progress.
 	 */
 	bool periodic_reclaim_paused;
-	int last_reclaim_threshold;
+	u8 last_reclaim_threshold;
 	u64 last_reclaim_unused;
 };
 
@@ -298,7 +298,7 @@ void btrfs_dump_space_info_for_trans_abort(struct btrfs_fs_info *fs_info);
 void btrfs_init_async_reclaim_work(struct btrfs_fs_info *fs_info);
 u64 btrfs_account_ro_block_groups_free_space(struct btrfs_space_info *sinfo);
 
-int btrfs_calc_reclaim_threshold(const struct btrfs_space_info *space_info);
+u8 btrfs_calc_reclaim_threshold(const struct btrfs_space_info *space_info);
 static inline void btrfs_resume_periodic_reclaim(struct btrfs_space_info *space_info)
 {
 	lockdep_assert_held(&space_info->lock);
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index f0974f4c0ae4..468c6a9acd3b 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -937,7 +937,8 @@ static ssize_t btrfs_sinfo_bg_reclaim_threshold_store(struct kobject *kobj,
 	if (thresh < 0 || thresh > 100)
 		return -EINVAL;
 
-	WRITE_ONCE(space_info->bg_reclaim_threshold, thresh);
+	/* Safe to case to u8 after checking thresh's range is between 0 and 100 */
+	WRITE_ONCE(space_info->bg_reclaim_threshold, (u8)thresh);
 
 	return len;
 }
-- 
2.51.2