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, 4 insertions, 5 deletions

diff --git a/fs/bcachefs/rebalance.h b/fs/bcachefs/rebalance.h
index 7ade0bb81cce..28a52638f16c 100644
--- a/fs/bcachefs/rebalance.h
+++ b/fs/bcachefs/rebalance.h
@@ -4,6 +4,9 @@
 
 #include "rebalance_types.h"
 
+int bch2_set_rebalance_needs_scan(struct bch_fs *, u64 inum);
+int bch2_set_fs_needs_rebalance(struct bch_fs *);
+
 static inline void rebalance_wakeup(struct bch_fs *c)
 {
 	struct task_struct *p;
@@ -15,11 +18,7 @@ static inline void rebalance_wakeup(struct bch_fs *c)
 	rcu_read_unlock();
 }
 
-void bch2_rebalance_add_key(struct bch_fs *, struct bkey_s_c,
-			    struct bch_io_opts *);
-void bch2_rebalance_add_work(struct bch_fs *, u64);
-
-void bch2_rebalance_work_to_text(struct printbuf *, struct bch_fs *);
+void bch2_rebalance_status_to_text(struct printbuf *, struct bch_fs *);
 
 void bch2_rebalance_stop(struct bch_fs *);
 int bch2_rebalance_start(struct bch_fs *);