bcachefs: Issue discards when needed to allocate journal write

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

fs/bcachefs/journal_io.c

@@ -1042,9 +1042,16 @@ void bch2_journal_write(struct closure *cl)
 	bytes = vstruct_bytes(jset);
 	memset((void *) jset + bytes, 0, (sectors << 9) - bytes);
 
+retry_alloc:
 	spin_lock(&j->lock);
 	ret = journal_write_alloc(j, w, sectors);
 
+	if (ret && j->can_discard) {
+		spin_unlock(&j->lock);
+		bch2_journal_do_discards(j);
+		goto retry_alloc;
+	}
+
 	/*
 	 * write is allocated, no longer need to account for it in
 	 * bch2_journal_space_available():