Commit a6548c8b authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcachefs: Avoid flushing the journal in the discard path 



When issuing discards, we may need to flush the journal if there's too
many buckets that can't be discarded until a journal flush.

But the heuristic was bad; we should be comparing the number of buckets
that need to flushes against the number of free buckets, not the number
of buckets we saw.

Signed-off-by: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 189c176c

fs/bcachefs/alloc_background.c

+41 −19
Original line number Diff line number Diff line
@@ -1604,13 +1604,36 @@ int bch2_check_alloc_to_lru_refs(struct bch_fs *c) 
	return ret;

}



struct discard_buckets_state {

	u64		seen;

	u64		open;

	u64		need_journal_commit;

	u64		discarded;

	struct bch_dev	*ca;

	u64		need_journal_commit_this_dev;

};



static void discard_buckets_next_dev(struct bch_fs *c, struct discard_buckets_state *s, struct bch_dev *ca)

{

	if (s->ca == ca)

		return;



	if (s->ca && s->need_journal_commit_this_dev >

	    bch2_dev_usage_read(s->ca).d[BCH_DATA_free].buckets)

		bch2_journal_flush_async(&c->journal, NULL);



	if (s->ca)

		percpu_ref_put(&s->ca->ref);

	if (ca)

		percpu_ref_get(&ca->ref);

	s->ca = ca;

	s->need_journal_commit_this_dev = 0;

}



static int bch2_discard_one_bucket(struct btree_trans *trans,

				   struct btree_iter *need_discard_iter,

				   struct bpos *discard_pos_done,

				   u64 *seen,

				   u64 *open,

				   u64 *need_journal_commit,

				   u64 *discarded)

				   struct discard_buckets_state *s)

{

	struct bch_fs *c = trans->c;

	struct bpos pos = need_discard_iter->pos;
@@ -1622,20 +1645,24 @@ static int bch2_discard_one_bucket(struct btree_trans *trans, 
	int ret = 0;



	ca = bch_dev_bkey_exists(c, pos.inode);



	if (!percpu_ref_tryget(&ca->io_ref)) {

		bch2_btree_iter_set_pos(need_discard_iter, POS(pos.inode + 1, 0));

		return 0;

	}



	discard_buckets_next_dev(c, s, ca);



	if (bch2_bucket_is_open_safe(c, pos.inode, pos.offset)) {

		(*open)++;

		s->open++;

		goto out;

	}



	if (bch2_bucket_needs_journal_commit(&c->buckets_waiting_for_journal,

			c->journal.flushed_seq_ondisk,

			pos.inode, pos.offset)) {

		(*need_journal_commit)++;

		s->need_journal_commit++;

		s->need_journal_commit_this_dev++;

		goto out;

	}
@@ -1711,9 +1738,9 @@ static int bch2_discard_one_bucket(struct btree_trans *trans, 
		goto out;



	count_event(c, bucket_discard);

	(*discarded)++;

	s->discarded++;

out:

	(*seen)++;

	s->seen++;

	bch2_trans_iter_exit(trans, &iter);

	percpu_ref_put(&ca->io_ref);

	printbuf_exit(&buf);
@@ -1723,7 +1750,7 @@ static int bch2_discard_one_bucket(struct btree_trans *trans, 
static void bch2_do_discards_work(struct work_struct *work)

{

	struct bch_fs *c = container_of(work, struct bch_fs, discard_work);

	u64 seen = 0, open = 0, need_journal_commit = 0, discarded = 0;

	struct discard_buckets_state s = {};

	struct bpos discard_pos_done = POS_MAX;

	int ret;
@@ -1735,19 +1762,14 @@ static void bch2_do_discards_work(struct work_struct *work) 
	ret = bch2_trans_run(c,

		for_each_btree_key(trans, iter,

				   BTREE_ID_need_discard, POS_MIN, 0, k,

			bch2_discard_one_bucket(trans, &iter, &discard_pos_done,

						&seen,

						&open,

						&need_journal_commit,

						&discarded)));



	if (need_journal_commit * 2 > seen)

		bch2_journal_flush_async(&c->journal, NULL);

			bch2_discard_one_bucket(trans, &iter, &discard_pos_done, &s)));



	bch2_write_ref_put(c, BCH_WRITE_REF_discard);

	discard_buckets_next_dev(c, &s, NULL);



	trace_discard_buckets(c, seen, open, need_journal_commit, discarded,

	trace_discard_buckets(c, s.seen, s.open, s.need_journal_commit, s.discarded,

			      bch2_err_str(ret));



	bch2_write_ref_put(c, BCH_WRITE_REF_discard);

}



void bch2_do_discards(struct bch_fs *c)