btrfs: zoned: enable metadata over-commit for non-ZNS setup

The commit 79417d04 ("btrfs: zoned: disable metadata overcommit for
zoned") disabled the metadata over-commit to track active zones properly.

However, it also introduced a heavy overhead by allocating new metadata
block groups and/or flushing dirty buffers to release the space
reservations. Specifically, a workload (write only without any sync
operations) worsen its performance from 343.77 MB/sec (v5.19) to 182.89
MB/sec (v6.0).

The performance is still bad on current misc-next which is 187.95 MB/sec.
And, with this patch applied, it improves back to 326.70 MB/sec (+73.82%).

This patch introduces a new fs_info->flag BTRFS_FS_NO_OVERCOMMIT to
indicate it needs to disable the metadata over-commit. The flag is enabled
when a device with max active zones limit is loaded into a file-system.

Fixes: 79417d04 ("btrfs: zoned: disable metadata overcommit for zoned")
CC: stable@vger.kernel.org # 6.0+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/fs.h

@@ -119,6 +119,12 @@ enum {
 	/* Indicate that we want to commit the transaction. */
 	BTRFS_FS_NEED_TRANS_COMMIT,
 
+	/*
+	 * Indicate metadata over-commit is disabled. This is set when active
+	 * zone tracking is needed.
+	 */
+	BTRFS_FS_NO_OVERCOMMIT,
+
 #if BITS_PER_LONG == 32
 	/* Indicate if we have error/warn message printed on 32bit systems */
 	BTRFS_FS_32BIT_ERROR,

fs/btrfs/space-info.c

@@ -407,7 +407,8 @@ int btrfs_can_overcommit(struct btrfs_fs_info *fs_info,
 		return 0;
 
 	used = btrfs_space_info_used(space_info, true);
-	if (btrfs_is_zoned(fs_info) && (space_info->flags & BTRFS_BLOCK_GROUP_METADATA))
+	if (test_bit(BTRFS_FS_NO_OVERCOMMIT, &fs_info->flags) &&
+	    (space_info->flags & BTRFS_BLOCK_GROUP_METADATA))
 		avail = 0;
 	else
 		avail = calc_available_free_space(fs_info, space_info, flush);

fs/btrfs/zoned.c

@@ -539,6 +539,8 @@ int btrfs_get_dev_zone_info(struct btrfs_device *device, bool populate_cache)
 		}
 		atomic_set(&zone_info->active_zones_left,
 			   max_active_zones - nactive);
+		/* Overcommit does not work well with active zone tacking. */
+		set_bit(BTRFS_FS_NO_OVERCOMMIT, &fs_info->flags);
 	}
 
 	/* Validate superblock log */