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, 20 insertions, 0 deletions

diff --git a/fs/bcachefs/extents.h b/fs/bcachefs/extents.h
index ef1b9f18719d..9110acae7e3c 100644
--- a/fs/bcachefs/extents.h
+++ b/fs/bcachefs/extents.h
@@ -89,6 +89,18 @@ static inline void __extent_entry_insert(struct bkey_i *k,
 	memcpy_u64s_small(dst, new, extent_entry_u64s(new));
 }
 
+static inline void extent_entry_drop(struct bkey_s k, union bch_extent_entry *entry)
+{
+	union bch_extent_entry *next = extent_entry_next(entry);
+
+	/* stripes have ptrs, but their layout doesn't work with this code */
+	BUG_ON(k.k->type == KEY_TYPE_stripe);
+
+	memmove_u64s_down(entry, next,
+			  (u64 *) bkey_val_end(k) - (u64 *) next);
+	k.k->u64s -= (u64 *) next - (u64 *) entry;
+}
+
 static inline bool extent_entry_is_ptr(const union bch_extent_entry *e)
 {
 	return extent_entry_type(e) == BCH_EXTENT_ENTRY_ptr;
@@ -698,6 +710,14 @@ int bch2_bkey_ptrs_invalid(const struct bch_fs *, struct bkey_s_c,
 
 void bch2_ptr_swab(struct bkey_s);
 
+const struct bch_extent_rebalance *bch2_bkey_rebalance_opts(struct bkey_s_c);
+unsigned bch2_bkey_ptrs_need_rebalance(struct bch_fs *, struct bkey_s_c,
+				       unsigned, unsigned);
+bool bch2_bkey_needs_rebalance(struct bch_fs *, struct bkey_s_c);
+
+int bch2_bkey_set_needs_rebalance(struct bch_fs *, struct bkey_i *,
+				  unsigned, unsigned);
+
 /* Generic extent code: */
 
 enum bch_extent_overlap {