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, 6 insertions, 8 deletions

diff --git a/fs/bcachefs/sysfs.c b/fs/bcachefs/sysfs.c
index 3ac6634020d1..7975587cab9a 100644
--- a/fs/bcachefs/sysfs.c
+++ b/fs/bcachefs/sysfs.c
@@ -212,7 +212,7 @@ read_attribute(copy_gc_wait);
 
 rw_attribute(rebalance_enabled);
 sysfs_pd_controller_attribute(rebalance);
-read_attribute(rebalance_work);
+read_attribute(rebalance_status);
 rw_attribute(promote_whole_extents);
 
 read_attribute(new_stripes);
@@ -386,8 +386,8 @@ SHOW(bch2_fs)
 	if (attr == &sysfs_copy_gc_wait)
 		bch2_copygc_wait_to_text(out, c);
 
-	if (attr == &sysfs_rebalance_work)
-		bch2_rebalance_work_to_text(out, c);
+	if (attr == &sysfs_rebalance_status)
+		bch2_rebalance_status_to_text(out, c);
 
 	sysfs_print(promote_whole_extents,	c->promote_whole_extents);
 
@@ -646,7 +646,7 @@ struct attribute *bch2_fs_internal_files[] = {
 	&sysfs_copy_gc_wait,
 
 	&sysfs_rebalance_enabled,
-	&sysfs_rebalance_work,
+	&sysfs_rebalance_status,
 	sysfs_pd_controller_files(rebalance),
 
 	&sysfs_moving_ctxts,
@@ -707,10 +707,8 @@ STORE(bch2_fs_opts_dir)
 	bch2_opt_set_by_id(&c->opts, id, v);
 
 	if ((id == Opt_background_target ||
-	     id == Opt_background_compression) && v) {
-		bch2_rebalance_add_work(c, S64_MAX);
-		rebalance_wakeup(c);
-	}
+	     id == Opt_background_compression) && v)
+		bch2_set_rebalance_needs_scan(c, 0);
 
 	ret = size;
 err: