bcachefs: New discard implementation

In the old allocator code, buckets would be discarded just prior to
being used - this made sense in bcache where we were discarding buckets
just after invalidating the cached data they contain, but in a
filesystem where we typically have more free space we want to be
discarding buckets when they become empty.

This patch implements the new behaviour - it checks the need_discard
btree for buckets awaiting discards, and then clears the appropriate
bit in the alloc btree, which moves the buckets to the freespace btree.

Additionally, discards are now enabled by default.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
index 74b23f9b1bd3..8ba9bf853c2f 100644
--- a/fs/bcachefs/alloc_background.h
+++ b/fs/bcachefs/alloc_background.h
@@ -113,6 +113,8 @@ int bch2_alloc_read(struct bch_fs *, bool, bool);
 
 int bch2_trans_mark_alloc(struct btree_trans *, struct bkey_s_c,
 			  struct bkey_i *, unsigned);
+void bch2_do_discards(struct bch_fs *);
+
 int bch2_fs_freespace_init(struct bch_fs *);
 
 void bch2_recalc_capacity(struct bch_fs *);