[PATCH RFC 9/9] btrfs: remove unused bgs on allocation failure

[Johannes Thumshirn <jth@kernel.org>]

From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

In case find_free_extent() return ENOSPC, check if there are block-groups
in the filsystem which have been marked as 'unused' and if so, reclaim the
space occupied by these block-groups.

Restart the search for free space to place the extent afterwards.

In case the allocation is targeted for the data relocation root, skip this
step, as it can cause deadlocks between block group deletion and relocation.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/block-group.h | 11 +++++++++++
 fs/btrfs/extent-tree.c |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index a8bb8429c966..d5c91db88456 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -396,4 +396,15 @@ int btrfs_use_block_group_size_class(struct btrfs_block_group *bg,
 				     bool force_wrong_size_class);
 bool btrfs_block_group_should_use_size_class(const struct btrfs_block_group *bg);
 
+static inline bool btrfs_has_unused_block_groups(struct btrfs_fs_info *fs_info)
+{
+	bool unused_bgs;
+
+	spin_lock(&fs_info->unused_bgs_lock);
+	unused_bgs = !list_empty(&fs_info->unused_bgs);
+	spin_unlock(&fs_info->unused_bgs_lock);
+
+	return unused_bgs;
+}
+
 #endif /* BTRFS_BLOCK_GROUP_H */
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index da731f6d4dad..34d21713c6ab 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4683,6 +4683,11 @@ int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes,
 	if (!ret && !is_data) {
 		btrfs_dec_block_group_reservations(fs_info, ins->objectid);
 	} else if (ret == -ENOSPC) {
+		if (!btrfs_is_data_reloc_root(root) &&
+		    btrfs_has_unused_block_groups(fs_info)) {
+			btrfs_delete_unused_bgs(fs_info);
+			goto again;
+		}
 		if (!final_tried && ins->offset) {
 			num_bytes = min(num_bytes >> 1, ins->offset);
 			num_bytes = round_down(num_bytes,
-- 
2.49.0