bcachefs: rebalance_work

This adds a new btree, rebalance_work, to eliminate scanning required
for finding extents that need work done on them in the background - i.e.
for the background_target and background_compression options.

rebalance_work is a bitset btree, where a KEY_TYPE_set corresponds to an
extent in the extents or reflink btree at the same pos.

A new extent field is added, bch_extent_rebalance, which indicates that
this extent has work that needs to be done in the background - and which
options to use. This allows per-inode options to be propagated to
indirect extents - at least in some circumstances. In this patch,
changing IO options on a file will not propagate the new options to
indirect extents pointed to by that file.

Updating (setting/clearing) the rebalance_work btree is done by the
extent trigger, which looks at the bch_extent_rebalance field.

Scanning is still requrired after changing IO path options - either just
for a given inode, or for the whole filesystem. We indicate that
scanning is required by adding a KEY_TYPE_cookie key to the
rebalance_work btree: the cookie counter is so that we can detect that
scanning is still required when an option has been flipped mid-way
through an existing scan.

Future possible work:
 - Propagate options to indirect extents when being changed
 - Add other IO path options - nr_replicas, ec, to rebalance_work so
   they can be applied in the background when they change
 - Add a counter, for bcachefs fs usage output, showing the pending
   amount of rebalance work: we'll probably want to do this after the
   disk space accounting rewrite (moving it to a new btree)

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 12 insertions, 22 deletions

diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h
index 99749f3315fe..e04999c57892 100644
--- a/fs/bcachefs/bcachefs_format.h
+++ b/fs/bcachefs/bcachefs_format.h
@@ -613,31 +613,17 @@ struct bch_extent_stripe_ptr {
 #endif
 };
 
-struct bch_extent_reservation {
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	__u64			type:6,
-				unused:22,
-				replicas:4,
-				generation:32;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	__u64			generation:32,
-				replicas:4,
-				unused:22,
-				type:6;
-#endif
-};
-
 struct bch_extent_rebalance {
 #if defined(__LITTLE_ENDIAN_BITFIELD)
-	__u64			type:7,
-				unused:33,
-				compression:8,
+	__u64			type:6,
+				unused:34,
+				compression:8, /* enum bch_compression_opt */
 				target:16;
 #elif defined (__BIG_ENDIAN_BITFIELD)
 	__u64			target:16,
 				compression:8,
-				unused:33,
-				type:7;
+				unused:34,
+				type:6;
 #endif
 };
 
@@ -1682,7 +1668,9 @@ struct bch_sb_field_journal_seq_blacklist {
 	x(snapshot_skiplists,		BCH_VERSION(1,  1),		\
 	  BIT_ULL(BCH_RECOVERY_PASS_check_snapshots))			\
 	x(deleted_inodes,		BCH_VERSION(1,  2),		\
-	  BIT_ULL(BCH_RECOVERY_PASS_check_inodes))
+	  BIT_ULL(BCH_RECOVERY_PASS_check_inodes))			\
+	x(rebalance_work,		BCH_VERSION(1,  3),		\
+	  BIT_ULL(BCH_RECOVERY_PASS_set_fs_needs_rebalance))
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,
@@ -1693,7 +1681,7 @@ enum bcachefs_metadata_version {
 };
 
 static const __maybe_unused
-unsigned bcachefs_metadata_required_upgrade_below = bcachefs_metadata_version_major_minor;
+unsigned bcachefs_metadata_required_upgrade_below = bcachefs_metadata_version_rebalance_work;
 
 #define bcachefs_metadata_version_current	(bcachefs_metadata_version_max - 1)
 
@@ -2306,7 +2294,9 @@ enum btree_id_flags {
 	  BIT_ULL(KEY_TYPE_set))						\
 	x(logged_ops,		17,	0,					\
 	  BIT_ULL(KEY_TYPE_logged_op_truncate)|					\
-	  BIT_ULL(KEY_TYPE_logged_op_finsert))
+	  BIT_ULL(KEY_TYPE_logged_op_finsert))					\
+	x(rebalance_work,	18,	BTREE_ID_SNAPSHOTS,			\
+	  BIT_ULL(KEY_TYPE_set)|BIT_ULL(KEY_TYPE_cookie))
 
 enum btree_id {
 #define x(name, nr, ...) BTREE_ID_##name = nr,