[PATCH v5] btrfs: zoned: reserve data_reloc block group on mount

[Johannes Thumshirn <jth@kernel.org>]

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

Create a block group dedicated for data relocation on mount of a zoned
filesystem.

If there is already more than one empty DATA block group on mount, this
one is picked for the data relocation block group, instead of a newly
created one.

This is done to ensure, there is always space for performing garbage
collection and the filesystem is not hitting ENOSPC under heavy overwrite
workloads.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
Changes to v4:
- Use btrfs_commit_transaction() instead of btrfs_end_transaction

 fs/btrfs/disk-io.c |  1 +
 fs/btrfs/zoned.c   | 61 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/zoned.h   |  3 +++
 3 files changed, 65 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3def93016963..b211dc8cdb86 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3562,6 +3562,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 		goto fail_sysfs;
 	}
 
+	btrfs_zoned_reserve_data_reloc_bg(fs_info);
 	btrfs_free_zone_cache(fs_info);
 
 	btrfs_check_active_zone_reservation(fs_info);
diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 19710634d63f..4e122d6c19c0 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -17,6 +17,7 @@
 #include "fs.h"
 #include "accessors.h"
 #include "bio.h"
+#include "transaction.h"
 
 /* Maximum number of zones to report per blkdev_report_zones() call */
 #define BTRFS_REPORT_NR_ZONES   4096
@@ -2443,6 +2444,66 @@ void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg)
 	spin_unlock(&fs_info->relocation_bg_lock);
 }
 
+void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_space_info *data_sinfo = fs_info->data_sinfo;
+	struct btrfs_space_info *space_info = data_sinfo->sub_group[0];
+	struct btrfs_trans_handle *trans;
+	struct btrfs_block_group *bg;
+	struct list_head *bg_list;
+	u64 alloc_flags;
+	bool initial = false;
+	bool did_chunk_alloc = false;
+	int index;
+	int ret;
+
+	if (!btrfs_is_zoned(fs_info))
+		return;
+
+	if (fs_info->data_reloc_bg)
+		return;
+
+	if (sb_rdonly(fs_info->sb))
+		return;
+
+	ASSERT(space_info->subgroup_id == BTRFS_SUB_GROUP_DATA_RELOC);
+	alloc_flags = btrfs_get_alloc_profile(fs_info, space_info->flags);
+	index = btrfs_bg_flags_to_raid_index(alloc_flags);
+
+	bg_list = &data_sinfo->block_groups[index];
+again:
+	list_for_each_entry(bg, bg_list, list) {
+		if (bg->used > 0)
+			continue;
+
+		if (!initial) {
+			initial = true;
+			continue;
+		}
+
+		fs_info->data_reloc_bg = bg->start;
+		set_bit(BLOCK_GROUP_FLAG_ZONED_DATA_RELOC, &bg->runtime_flags);
+		btrfs_zone_activate(bg);
+
+		return;
+	}
+
+	if (did_chunk_alloc)
+		return;
+
+	trans = btrfs_join_transaction(fs_info->tree_root);
+	if (IS_ERR(trans))
+		return;
+
+	ret = btrfs_chunk_alloc(trans, space_info, alloc_flags, CHUNK_ALLOC_FORCE);
+	btrfs_commit_transaction(trans);
+	if (ret == 1) {
+		did_chunk_alloc = true;
+		bg_list = &space_info->block_groups[index];
+		goto again;
+	}
+}
+
 void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h
index 9672bf4c3335..6e11533b8e14 100644
--- a/fs/btrfs/zoned.h
+++ b/fs/btrfs/zoned.h
@@ -88,6 +88,7 @@ void btrfs_zone_finish_endio(struct btrfs_fs_info *fs_info, u64 logical,
 void btrfs_schedule_zone_finish_bg(struct btrfs_block_group *bg,
 				   struct extent_buffer *eb);
 void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg);
+void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info);
 void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info);
 bool btrfs_zoned_should_reclaim(const struct btrfs_fs_info *fs_info);
 void btrfs_zoned_release_data_reloc_bg(struct btrfs_fs_info *fs_info, u64 logical,
@@ -241,6 +242,8 @@ static inline void btrfs_schedule_zone_finish_bg(struct btrfs_block_group *bg,
 
 static inline void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg) { }
 
+static inline void btrfs_zoned_reserve_data_reloc_bg(struct btrfs_fs_info *fs_info) { }
+
 static inline void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info) { }
 
 static inline bool btrfs_zoned_should_reclaim(const struct btrfs_fs_info *fs_info)
-- 
2.49.0