bcachefs: bch2_journal_entries_postprocess()

This brings back journal_entries_compact(), but in a more efficient form
- we need to do multiple postprocess steps, so iterate over the
journal entries being written just once to make it more efficient.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_update_interior.c

@@ -2402,20 +2402,15 @@ bool bch2_btree_interior_updates_flush(struct bch_fs *c)
 	return ret;
 }
 
-void bch2_journal_entries_to_btree_roots(struct bch_fs *c, struct jset *jset)
+void bch2_journal_entry_to_btree_root(struct bch_fs *c, struct jset_entry *entry)
 {
-	struct btree_root *r;
-	struct jset_entry *entry;
+	struct btree_root *r = &c->btree_roots[entry->btree_id];
 
 	mutex_lock(&c->btree_root_lock);
 
-	vstruct_for_each(jset, entry)
-		if (entry->type == BCH_JSET_ENTRY_btree_root) {
-			r = &c->btree_roots[entry->btree_id];
 	r->level = entry->level;
 	r->alive = true;
 	bkey_copy(&r->key, &entry->start[0]);
-		}
 
 	mutex_unlock(&c->btree_root_lock);
 }

fs/bcachefs/btree_update_interior.h

@@ -314,7 +314,7 @@ void bch2_btree_updates_to_text(struct printbuf *, struct bch_fs *);
 
 bool bch2_btree_interior_updates_flush(struct bch_fs *);
 
-void bch2_journal_entries_to_btree_roots(struct bch_fs *, struct jset *);
+void bch2_journal_entry_to_btree_root(struct bch_fs *, struct jset_entry *);
 struct jset_entry *bch2_btree_roots_to_journal_entries(struct bch_fs *,
 					struct jset_entry *, struct jset_entry *);
 

fs/bcachefs/journal_io.c

@@ -1621,6 +1621,52 @@ static void do_journal_write(struct closure *cl)
 	return;
 }
 
+static void bch2_journal_entries_postprocess(struct bch_fs *c, struct jset *jset)
+{
+	struct jset_entry *i, *next, *prev = NULL;
+
+	/*
+	 * Simple compaction, dropping empty jset_entries (from journal
+	 * reservations that weren't fully used) and merging jset_entries that
+	 * can be.
+	 *
+	 * If we wanted to be really fancy here, we could sort all the keys in
+	 * the jset and drop keys that were overwritten - probably not worth it:
+	 */
+	vstruct_for_each_safe(jset, i, next) {
+		unsigned u64s = le16_to_cpu(i->u64s);
+
+		/* Empty entry: */
+		if (!u64s)
+			continue;
+
+		if (i->type == BCH_JSET_ENTRY_btree_root)
+			bch2_journal_entry_to_btree_root(c, i);
+
+		/* Can we merge with previous entry? */
+		if (prev &&
+		    i->btree_id == prev->btree_id &&
+		    i->level	== prev->level &&
+		    i->type	== prev->type &&
+		    i->type	== BCH_JSET_ENTRY_btree_keys &&
+		    le16_to_cpu(prev->u64s) + u64s <= U16_MAX) {
+			memmove_u64s_down(vstruct_next(prev),
+					  i->_data,
+					  u64s);
+			le16_add_cpu(&prev->u64s, u64s);
+			continue;
+		}
+
+		/* Couldn't merge, move i into new position (after prev): */
+		prev = prev ? vstruct_next(prev) : jset->start;
+		if (i != prev)
+			memmove_u64s_down(prev, i, jset_u64s(u64s));
+	}
+
+	prev = prev ? vstruct_next(prev) : jset->start;
+	jset->u64s = cpu_to_le32((u64 *) prev - jset->_data);
+}
+
 void bch2_journal_write(struct closure *cl)
 {
 	struct journal *j = container_of(cl, struct journal, io);
@@ -1692,7 +1738,7 @@ void bch2_journal_write(struct closure *cl)
 	 * entry:
 	 */
 
-	bch2_journal_entries_to_btree_roots(c, jset);
+	bch2_journal_entries_postprocess(c, jset);
 
 	start = end = vstruct_last(jset);