btrfs: zoned: automatically reclaim zones

When a file gets deleted on a zoned file system, the space freed is not
returned back into the block group's free space, but is migrated to
zone_unusable.

As this zone_unusable space is behind the current write pointer it is not
possible to use it for new allocations. In the current implementation a
zone is reset once all of the block group's space is accounted as zone
unusable.

This behaviour can lead to premature ENOSPC errors on a busy file system.

Instead of only reclaiming the zone once it is completely unusable,
kick off a reclaim job once the amount of unusable bytes exceeds a user
configurable threshold between 51% and 100%. It can be set per mounted
filesystem via the sysfs tunable bg_reclaim_threshold which is set to 75%
by default.

Similar to reclaiming unused block groups, these dirty block groups are
added to a to_reclaim list and then on a transaction commit, the reclaim
process is triggered but after we deleted unused block groups, which will
free space for the relocation process.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 9988decd5717..e54466fc101f 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -11,6 +11,7 @@
 #include <linux/ratelimit.h>
 #include <linux/error-injection.h>
 #include <linux/sched/mm.h>
+#include "misc.h"
 #include "ctree.h"
 #include "free-space-cache.h"
 #include "transaction.h"
@@ -2539,6 +2540,7 @@ 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_free_space_ctl *ctl = block_group->free_space_ctl;
 	u64 offset = bytenr - block_group->start;
 	u64 to_free, to_unusable;
@@ -2569,8 +2571,13 @@ static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
 	}
 
 	/* All the region is now unusable. Mark it as unused and reclaim */
-	if (block_group->zone_unusable == block_group->length)
+	if (block_group->zone_unusable == block_group->length) {
 		btrfs_mark_bg_unused(block_group);
+	} else if (block_group->zone_unusable >=
+		   div_factor_fine(block_group->length,
+				   fs_info->bg_reclaim_threshold)) {
+		btrfs_mark_bg_to_reclaim(block_group);
+	}
 
 	return 0;
 }