bcachefs: bch2_journal_noflush_seq()

Add bch2_journal_noflush_seq(), for telling the journal that entries
before a given sequence number should not be flushes - to be used by an
upcoming allocator optimization.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/journal.c

@@ -704,6 +704,44 @@ int bch2_journal_flush(struct journal *j)
 	return bch2_journal_flush_seq(j, seq);
 }
 
+/*
+ * bch2_journal_noflush_seq - tell the journal not to issue any flushes before
+ * @seq
+ */
+bool bch2_journal_noflush_seq(struct journal *j, u64 seq)
+{
+	struct bch_fs *c = container_of(j, struct bch_fs, journal);
+	u64 unwritten_seq;
+	bool ret = false;
+
+	if (!(c->sb.features & (1ULL << BCH_FEATURE_journal_no_flush)))
+		return false;
+
+	if (seq <= c->journal.flushed_seq_ondisk)
+		return false;
+
+	spin_lock(&j->lock);
+	if (seq <= c->journal.flushed_seq_ondisk)
+		goto out;
+
+	for (unwritten_seq = last_unwritten_seq(j);
+	     unwritten_seq < seq;
+	     unwritten_seq++) {
+		struct journal_buf *buf = journal_seq_to_buf(j, unwritten_seq);
+
+		/* journal write is already in flight, and was a flush write: */
+		if (unwritten_seq == last_unwritten_seq(j) && !buf->noflush)
+			goto out;
+
+		buf->noflush = true;
+	}
+
+	ret = true;
+out:
+	spin_unlock(&j->lock);
+	return ret;
+}
+
 /* block/unlock the journal: */
 
 void bch2_journal_unblock(struct journal *j)

fs/bcachefs/journal.h

@@ -475,6 +475,7 @@ void bch2_journal_flush_async(struct journal *, struct closure *);
 
 int bch2_journal_flush_seq(struct journal *, u64);
 int bch2_journal_flush(struct journal *);
+bool bch2_journal_noflush_seq(struct journal *, u64);
 int bch2_journal_meta(struct journal *);
 
 void bch2_journal_halt(struct journal *);

fs/bcachefs/journal_io.c

@@ -1396,9 +1396,10 @@ void bch2_journal_write(struct closure *cl)
 
 	spin_lock(&j->lock);
 	if (c->sb.features & (1ULL << BCH_FEATURE_journal_no_flush) &&
-	    !w->must_flush &&
-	    (jiffies - j->last_flush_write) < msecs_to_jiffies(c->opts.journal_flush_delay) &&
-	    test_bit(JOURNAL_MAY_SKIP_FLUSH, &j->flags)) {
+	    (w->noflush ||
+	     (!w->must_flush &&
+	      (jiffies - j->last_flush_write) < msecs_to_jiffies(c->opts.journal_flush_delay) &&
+	      test_bit(JOURNAL_MAY_SKIP_FLUSH, &j->flags)))) {
 		w->noflush = true;
 		SET_JSET_NO_FLUSH(jset, true);
 		jset->last_seq	= 0;