btrfs: make the bg_reclaim_threshold per-space info

For non-zoned file systems it's useful to have the auto reclaim feature,
however there are different use cases for non-zoned, for example we may
not want to reclaim metadata chunks ever, only data chunks.  Move this
sysfs flag to per-space_info.  This won't affect current users because
this tunable only ever did anything for zoned, and that is currently
hidden behind BTRFS_CONFIG_DEBUG.

Tested-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[ jth restore global bg_reclaim_threshold ]
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

@@ -2630,16 +2630,19 @@ out:
 static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
 					u64 bytenr, u64 size, bool used)
 {
-	struct btrfs_fs_info *fs_info = block_group->fs_info;
+	struct btrfs_space_info *sinfo = block_group->space_info;
 	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);
+	int bg_reclaim_threshold = 0;
 	bool initial = (size == block_group->length);
 	u64 reclaimable_unusable;
 
 	WARN_ON(!initial && offset + size > block_group->zone_capacity);
 
+	if (!initial)
+		bg_reclaim_threshold = READ_ONCE(sinfo->bg_reclaim_threshold);
+
 	spin_lock(&ctl->tree_lock);
 	if (!used)
 		to_free = size;

fs/btrfs/space-info.c

@@ -181,6 +181,12 @@ void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
 		found->full = 0;
 }
 
+/*
+ * Block groups with more than this value (percents) of unusable space will be
+ * scheduled for background reclaim.
+ */
+#define BTRFS_DEFAULT_ZONED_RECLAIM_THRESH			(75)
+
 static int create_space_info(struct btrfs_fs_info *info, u64 flags)
 {
 
@@ -203,6 +209,9 @@ static int create_space_info(struct btrfs_fs_info *info, u64 flags)
 	INIT_LIST_HEAD(&space_info->priority_tickets);
 	space_info->clamp = 1;
 
+	if (btrfs_is_zoned(info))
+		space_info->bg_reclaim_threshold = BTRFS_DEFAULT_ZONED_RECLAIM_THRESH;
+
 	ret = btrfs_sysfs_add_space_info_type(info, space_info);
 	if (ret)
 		return ret;

fs/btrfs/space-info.h

@@ -24,6 +24,12 @@ struct btrfs_space_info {
 				   the space info if we had an ENOSPC in the
 				   allocator. */
 
+	/*
+	 * 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. */

fs/btrfs/sysfs.c

@@ -720,6 +720,42 @@ SPACE_INFO_ATTR(bytes_zone_unusable);
 SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
 
+static ssize_t btrfs_sinfo_bg_reclaim_threshold_show(struct kobject *kobj,
+						     struct kobj_attribute *a,
+						     char *buf)
+{
+	struct btrfs_space_info *space_info = to_space_info(kobj);
+	ssize_t ret;
+
+	ret = sysfs_emit(buf, "%d\n", READ_ONCE(space_info->bg_reclaim_threshold));
+
+	return ret;
+}
+
+static ssize_t btrfs_sinfo_bg_reclaim_threshold_store(struct kobject *kobj,
+						      struct kobj_attribute *a,
+						      const char *buf, size_t len)
+{
+	struct btrfs_space_info *space_info = to_space_info(kobj);
+	int thresh;
+	int ret;
+
+	ret = kstrtoint(buf, 10, &thresh);
+	if (ret)
+		return ret;
+
+	if (thresh != 0 && (thresh <= 50 || thresh > 100))
+		return -EINVAL;
+
+	WRITE_ONCE(space_info->bg_reclaim_threshold, thresh);
+
+	return len;
+}
+
+BTRFS_ATTR_RW(space_info, bg_reclaim_threshold,
+	      btrfs_sinfo_bg_reclaim_threshold_show,
+	      btrfs_sinfo_bg_reclaim_threshold_store);
+
 /*
  * Allocation information about block group types.
  *
@@ -736,6 +772,7 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, bytes_zone_unusable),
 	BTRFS_ATTR_PTR(space_info, disk_used),
 	BTRFS_ATTR_PTR(space_info, disk_total),
+	BTRFS_ATTR_PTR(space_info, bg_reclaim_threshold),
 	NULL,
 };
 ATTRIBUTE_GROUPS(space_info);

fs/btrfs/zoned.h

@@ -10,11 +10,7 @@
 #include "block-group.h"
 #include "btrfs_inode.h"
 
-/*
- * Block groups with more than this value (percents) of unusable space will be
- * scheduled for background reclaim.
- */
-#define BTRFS_DEFAULT_RECLAIM_THRESH		75
+#define BTRFS_DEFAULT_RECLAIM_THRESH           			(75)
 
 struct btrfs_zoned_device_info {
 	/*