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From: Johannes Thumshirn <jth@kernel.org>
Date: Wed, 15 May 2024 20:43:06 +0200
Subject: [PATCH v2 1/2] btrfs: zoned: reserve relocation zone on mount
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Message-Id: <20240515-zoned-gc-v2-1-20c7cb9763cd@kernel.org>
References: <20240515-zoned-gc-v2-0-20c7cb9763cd@kernel.org>
In-Reply-To: <20240515-zoned-gc-v2-0-20c7cb9763cd@kernel.org>
To: Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>, 
 David Sterba <dsterba@suse.com>
Cc: Hans Holmberg <Hans.Holmberg@wdc.com>, linux-btrfs@vger.kernel.org, 
 linux-kernel@vger.kernel.org, Naohiro Aota <naohiro.aota@wdc.com>, 
 Johannes Thumshirn <johannes.thumshirn@wdc.com>

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

Reserve one zone as a data relocation target on each mount. If we already
find one empty block group, there's no need to force a chunk allocation,
but we can use this empty data block group as our relocation target.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/disk-io.c |  2 ++
 fs/btrfs/zoned.c   | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 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 a91a8056758a..0490f2f45fb1 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3558,6 +3558,8 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 	}
 	btrfs_discard_resume(fs_info);
 
+	btrfs_reserve_relocation_zone(fs_info);
+
 	if (fs_info->uuid_root &&
 	    (btrfs_test_opt(fs_info, RESCAN_UUID_TREE) ||
 	     fs_info->generation != btrfs_super_uuid_tree_generation(disk_super))) {
diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 4cba80b34387..b752f8c95f40 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
@@ -2634,3 +2635,62 @@ void btrfs_check_active_zone_reservation(struct btrfs_fs_info *fs_info)
 	}
 	spin_unlock(&fs_info->zone_active_bgs_lock);
 }
+
+static u64 find_empty_block_group(struct btrfs_space_info *sinfo, u64 flags)
+{
+	struct btrfs_block_group *bg;
+
+	for (int i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
+		list_for_each_entry(bg, &sinfo->block_groups[i], list) {
+			if (bg->flags != flags)
+				continue;
+			if (bg->used == 0)
+				return bg->start;
+		}
+	}
+
+	return 0;
+}
+
+void btrfs_reserve_relocation_zone(struct btrfs_fs_info *fs_info)
+{
+	struct btrfs_root *tree_root = fs_info->tree_root;
+	struct btrfs_space_info *sinfo = fs_info->data_sinfo;
+	struct btrfs_trans_handle *trans;
+	u64 flags = btrfs_get_alloc_profile(fs_info, sinfo->flags);
+	u64 bytenr = 0;
+
+	lockdep_assert_not_held(&fs_info->relocation_bg_lock);
+
+	if (!btrfs_is_zoned(fs_info))
+		return;
+
+	bytenr = find_empty_block_group(sinfo, flags);
+	if (!bytenr) {
+		int ret;
+
+		trans = btrfs_join_transaction(tree_root);
+		if (IS_ERR(trans))
+			return;
+
+		ret = btrfs_chunk_alloc(trans, flags, CHUNK_ALLOC_FORCE);
+		btrfs_end_transaction(trans);
+
+		if (!ret) {
+			struct btrfs_block_group *bg;
+
+			bytenr = find_empty_block_group(sinfo, flags);
+			if (!bytenr)
+				goto out;
+			bg = btrfs_lookup_block_group(fs_info, bytenr);
+			ASSERT(bg);
+
+			if (!btrfs_zone_activate(bg))
+				bytenr = 0;
+			btrfs_put_block_group(bg);
+		}
+	}
+
+out:
+	fs_info->data_reloc_bg = bytenr;
+}
diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h
index 77c4321e331f..048ffada4549 100644
--- a/fs/btrfs/zoned.h
+++ b/fs/btrfs/zoned.h
@@ -97,6 +97,7 @@ int btrfs_zone_finish_one_bg(struct btrfs_fs_info *fs_info);
 int btrfs_zoned_activate_one_bg(struct btrfs_fs_info *fs_info,
 				struct btrfs_space_info *space_info, bool do_finish);
 void btrfs_check_active_zone_reservation(struct btrfs_fs_info *fs_info);
+void btrfs_reserve_relocation_zone(struct btrfs_fs_info *fs_info);
 #else /* CONFIG_BLK_DEV_ZONED */
 static inline int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
 				     struct blk_zone *zone)
@@ -271,6 +272,8 @@ static inline int btrfs_zoned_activate_one_bg(struct btrfs_fs_info *fs_info,
 
 static inline void btrfs_check_active_zone_reservation(struct btrfs_fs_info *fs_info) { }
 
+static inline void btrfs_reserve_relocation_zone(struct btrfs_fs_info *fs_info) { }
+
 #endif
 
 static inline bool btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)

-- 
2.35.3