btrfs: zoned: allow disabling of zone auto reclaim

Automatically reclaiming dirty zones might not always be desired for all
workloads, especially as there are currently still some rough edges with
the relocation code on zoned filesystems.

Allow disabling zone auto reclaim on a per filesystem basis by writing 0
as the threshold value.
Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -2538,6 +2538,7 @@ static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
 	struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
 	u64 offset = bytenr - block_group->start;
 	u64 to_free, to_unusable;
+	const int bg_reclaim_threshold = READ_ONCE(fs_info->bg_reclaim_threshold);
 
 	spin_lock(&ctl->tree_lock);
 	if (!used)
@@ -2567,9 +2568,9 @@ static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
 	/* All the region is now unusable. Mark it as unused and reclaim */
 	if (block_group->zone_unusable == block_group->length) {
 		btrfs_mark_bg_unused(block_group);
-	} else if (block_group->zone_unusable >=
-		   div_factor_fine(block_group->length,
-				   fs_info->bg_reclaim_threshold)) {
+	} else if (bg_reclaim_threshold &&
+		   block_group->zone_unusable >=
+		   div_factor_fine(block_group->length, bg_reclaim_threshold)) {
 		btrfs_mark_bg_to_reclaim(block_group);
 	}
 

fs/btrfs/sysfs.c

@@ -984,7 +984,8 @@ static ssize_t btrfs_bg_reclaim_threshold_show(struct kobject *kobj,
 	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
 	ssize_t ret;
 
-	ret = scnprintf(buf, PAGE_SIZE, "%d\n", fs_info->bg_reclaim_threshold);
+	ret = scnprintf(buf, PAGE_SIZE, "%d\n",
+			READ_ONCE(fs_info->bg_reclaim_threshold));
 
 	return ret;
 }
@@ -1001,10 +1002,10 @@ static ssize_t btrfs_bg_reclaim_threshold_store(struct kobject *kobj,
 	if (ret)
 		return ret;
 
-	if (thresh <= 50 || thresh > 100)
+	if (thresh != 0 && (thresh <= 50 || thresh > 100))
 		return -EINVAL;
 
-	fs_info->bg_reclaim_threshold = thresh;
+	WRITE_ONCE(fs_info->bg_reclaim_threshold, thresh);
 
 	return len;
 }