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, 34 insertions, 0 deletions

diff --git a/fs/bcachefs/trace.h b/fs/bcachefs/trace.h
index caf59b977e2f..ef2096fd147d 100644
--- a/fs/bcachefs/trace.h
+++ b/fs/bcachefs/trace.h
@@ -182,6 +182,40 @@ TRACE_EVENT(journal_reclaim_finish,
 		  __entry->nr_flushed)
 );
 
+/* allocator: */
+
+TRACE_EVENT(do_discards,
+	TP_PROTO(struct bch_fs *c, u64 seen, u64 open,
+		 u64 need_journal_commit, u64 discarded, int ret),
+	TP_ARGS(c, seen, open, need_journal_commit, discarded, ret),
+
+	TP_STRUCT__entry(
+		__field(dev_t,		dev			)
+		__field(u64,		seen			)
+		__field(u64,		open			)
+		__field(u64,		need_journal_commit	)
+		__field(u64,		discarded		)
+		__field(int,		ret			)
+	),
+
+	TP_fast_assign(
+		__entry->dev			= c->dev;
+		__entry->seen			= seen;
+		__entry->open			= open;
+		__entry->need_journal_commit	= need_journal_commit;
+		__entry->discarded		= discarded;
+		__entry->ret			= ret;
+	),
+
+	TP_printk("%d%d seen %llu open %llu need_journal_commit %llu discarded %llu ret %i",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->seen,
+		  __entry->open,
+		  __entry->need_journal_commit,
+		  __entry->discarded,
+		  __entry->ret)
+);
+
 /* bset.c: */
 
 DEFINE_EVENT(bpos, bkey_pack_pos_fail,