From 6088234ce83acec4aaf56ecc0e9525bac18b4295 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Fri, 5 Apr 2024 23:27:27 -0400 Subject: [PATCH] bcachefs: JOURNAL_SPACE_LOW "bcachefs; Fix deadlock in bch2_btree_update_start()" was a significant performance regression (nearly 50%) on multithreaded random writes with fio. The reason is that the journal watermark checks multiple things, including the state of the btree write buffer, and on multithreaded update heavy workloads we're bottleneked on write buffer flushing - we don't want kicknig off btree updates to depend on the state of the write buffer. This isn't strictly correct; the interior btree update path does do write buffer updates, but it's a tiny fraction of total accounting updates and we're more concerned with space in the journal itself. Signed-off-by: Kent Overstreet --- fs/bcachefs/btree_key_cache.c | 2 +- fs/bcachefs/btree_update_interior.c | 18 +++++++----------- fs/bcachefs/journal_reclaim.c | 2 ++ fs/bcachefs/journal_types.h | 1 + fs/bcachefs/util.h | 8 ++++++++ 5 files changed, 19 insertions(+), 12 deletions(-) diff --git a/fs/bcachefs/btree_key_cache.c b/fs/bcachefs/btree_key_cache.c index 581edcb0911b..4ae7890f07c6 100644 --- a/fs/bcachefs/btree_key_cache.c +++ b/fs/bcachefs/btree_key_cache.c @@ -659,7 +659,7 @@ static int btree_key_cache_flush_pos(struct btree_trans *trans, commit_flags |= BCH_WATERMARK_reclaim; if (ck->journal.seq != journal_last_seq(j) || - j->watermark == BCH_WATERMARK_stripe) + !test_bit(JOURNAL_SPACE_LOW, &c->journal.flags)) commit_flags |= BCH_TRANS_COMMIT_no_journal_res; ret = bch2_btree_iter_traverse(&b_iter) ?: diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c index 24fbd5be70a2..a4a63e363047 100644 --- a/fs/bcachefs/btree_update_interior.c +++ b/fs/bcachefs/btree_update_interior.c @@ -1125,18 +1125,14 @@ bch2_btree_update_start(struct btree_trans *trans, struct btree_path *path, flags &= ~BCH_WATERMARK_MASK; flags |= watermark; - if (watermark < c->journal.watermark) { - struct journal_res res = { 0 }; - unsigned journal_flags = watermark|JOURNAL_RES_GET_CHECK; + if (watermark < BCH_WATERMARK_reclaim && + test_bit(JOURNAL_SPACE_LOW, &c->journal.flags)) { + if (flags & BCH_TRANS_COMMIT_journal_reclaim) + return ERR_PTR(-BCH_ERR_journal_reclaim_would_deadlock); - if ((flags & BCH_TRANS_COMMIT_journal_reclaim) && - watermark < BCH_WATERMARK_reclaim) - journal_flags |= JOURNAL_RES_GET_NONBLOCK; - - ret = drop_locks_do(trans, - bch2_journal_res_get(&c->journal, &res, 1, journal_flags)); - if (bch2_err_matches(ret, BCH_ERR_operation_blocked)) - ret = -BCH_ERR_journal_reclaim_would_deadlock; + bch2_trans_unlock(trans); + wait_event(c->journal.wait, !test_bit(JOURNAL_SPACE_LOW, &c->journal.flags)); + ret = bch2_trans_relock(trans); if (ret) return ERR_PTR(ret); } diff --git a/fs/bcachefs/journal_reclaim.c b/fs/bcachefs/journal_reclaim.c index ab811c0dad26..04a577848b01 100644 --- a/fs/bcachefs/journal_reclaim.c +++ b/fs/bcachefs/journal_reclaim.c @@ -67,6 +67,8 @@ void bch2_journal_set_watermark(struct journal *j) track_event_change(&c->times[BCH_TIME_blocked_write_buffer_full], low_on_wb)) trace_and_count(c, journal_full, c); + mod_bit(JOURNAL_SPACE_LOW, &j->flags, low_on_space || low_on_pin); + swap(watermark, j->watermark); if (watermark > j->watermark) journal_wake(j); diff --git a/fs/bcachefs/journal_types.h b/fs/bcachefs/journal_types.h index 8c053cb64ca5..b5161b5d76a0 100644 --- a/fs/bcachefs/journal_types.h +++ b/fs/bcachefs/journal_types.h @@ -134,6 +134,7 @@ enum journal_flags { JOURNAL_STARTED, JOURNAL_MAY_SKIP_FLUSH, JOURNAL_NEED_FLUSH_WRITE, + JOURNAL_SPACE_LOW, }; /* Reasons we may fail to get a journal reservation: */ diff --git a/fs/bcachefs/util.h b/fs/bcachefs/util.h index de639e8a3ab5..5cf885b09986 100644 --- a/fs/bcachefs/util.h +++ b/fs/bcachefs/util.h @@ -788,6 +788,14 @@ static inline int copy_from_user_errcode(void *to, const void __user *from, unsi #endif +static inline void mod_bit(long nr, volatile unsigned long *addr, bool v) +{ + if (v) + set_bit(nr, addr); + else + clear_bit(nr, addr); +} + static inline void __set_bit_le64(size_t bit, __le64 *addr) { addr[bit / 64] |= cpu_to_le64(BIT_ULL(bit % 64)); -- 2.39.5