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, 7 insertions, 13 deletions

diff --git a/fs/bcachefs/io_write.c b/fs/bcachefs/io_write.c
index f7461f60d760..6d9c777213e3 100644
--- a/fs/bcachefs/io_write.c
+++ b/fs/bcachefs/io_write.c
@@ -351,10 +351,13 @@ static int bch2_write_index_default(struct bch_write_op *op)
 				     bkey_start_pos(&sk.k->k),
 				     BTREE_ITER_SLOTS|BTREE_ITER_INTENT);
 
-		ret = bch2_extent_update(trans, inum, &iter, sk.k,
-					 &op->res,
-					 op->new_i_size, &op->i_sectors_delta,
-					 op->flags & BCH_WRITE_CHECK_ENOSPC);
+		ret =   bch2_bkey_set_needs_rebalance(c, sk.k,
+					op->opts.background_target,
+					op->opts.background_compression) ?:
+			bch2_extent_update(trans, inum, &iter, sk.k,
+					&op->res,
+					op->new_i_size, &op->i_sectors_delta,
+					op->flags & BCH_WRITE_CHECK_ENOSPC);
 		bch2_trans_iter_exit(trans, &iter);
 
 		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
@@ -495,7 +498,6 @@ static void __bch2_write_index(struct bch_write_op *op)
 {
 	struct bch_fs *c = op->c;
 	struct keylist *keys = &op->insert_keys;
-	struct bkey_i *k;
 	unsigned dev;
 	int ret = 0;
 
@@ -505,14 +507,6 @@ static void __bch2_write_index(struct bch_write_op *op)
 			goto err;
 	}
 
-	/*
-	 * probably not the ideal place to hook this in, but I don't
-	 * particularly want to plumb io_opts all the way through the btree
-	 * update stack right now
-	 */
-	for_each_keylist_key(keys, k)
-		bch2_rebalance_add_key(c, bkey_i_to_s_c(k), &op->opts);
-
 	if (!bch2_keylist_empty(keys)) {
 		u64 sectors_start = keylist_sectors(keys);