jbd: Refine commit writeout logic
Currently we write out all journal buffers in WRITE_SYNC mode. This improves performance for fsync heavy workloads but hinders performance when writes are mostly asynchronous, most noticably it slows down readers and users complain about slow desktop response etc. So submit writes as asynchronous in the normal case and only submit writes as WRITE_SYNC if we detect someone is waiting for current transaction commit. I've gathered some numbers to back this change. The first is the read latency test. It measures time to read 1 MB after several seconds of sleeping in presence of streaming writes. Top 10 times (out of 90) in us: Before After 2131586 697473 1709932 557487 1564598 535642 1480462 347573 1478579 323153 1408496 222181 1388960 181273 1329565 181070 1252486 172832 1223265 172278 Average: 619377 82180 So the improvement in both maximum and average latency is massive. I've measured fsync throughput by: fs_mark -n 100 -t 1 -s 16384 -d /mnt/fsync/ -S 1 -L 4 in presence of streaming reader. The numbers (fsyncs/s) are: Before After 9.9 6.3 6.8 6.0 6.3 6.2 5.8 6.1 So fsync performance seems unharmed by this change. Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara
parent
923e9a1399
commit
2db938bee3
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@ -298,6 +298,7 @@ void journal_commit_transaction(journal_t *journal)
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int tag_flag;
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int i;
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struct blk_plug plug;
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int write_op = WRITE;
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/*
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* First job: lock down the current transaction and wait for
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@ -413,13 +414,16 @@ void journal_commit_transaction(journal_t *journal)
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jbd_debug (3, "JBD: commit phase 2\n");
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if (tid_geq(journal->j_commit_waited, commit_transaction->t_tid))
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write_op = WRITE_SYNC;
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/*
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* Now start flushing things to disk, in the order they appear
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* on the transaction lists. Data blocks go first.
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*/
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blk_start_plug(&plug);
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err = journal_submit_data_buffers(journal, commit_transaction,
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WRITE_SYNC);
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write_op);
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blk_finish_plug(&plug);
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/*
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@ -478,7 +482,7 @@ void journal_commit_transaction(journal_t *journal)
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blk_start_plug(&plug);
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journal_write_revoke_records(journal, commit_transaction, WRITE_SYNC);
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journal_write_revoke_records(journal, commit_transaction, write_op);
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/*
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* If we found any dirty or locked buffers, then we should have
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@ -649,7 +653,7 @@ start_journal_io:
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clear_buffer_dirty(bh);
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set_buffer_uptodate(bh);
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bh->b_end_io = journal_end_buffer_io_sync;
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submit_bh(WRITE_SYNC, bh);
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submit_bh(write_op, bh);
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}
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cond_resched();
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@ -563,6 +563,8 @@ int log_wait_commit(journal_t *journal, tid_t tid)
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spin_unlock(&journal->j_state_lock);
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#endif
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spin_lock(&journal->j_state_lock);
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if (!tid_geq(journal->j_commit_waited, tid))
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journal->j_commit_waited = tid;
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while (tid_gt(tid, journal->j_commit_sequence)) {
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jbd_debug(1, "JBD: want %d, j_commit_sequence=%d\n",
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tid, journal->j_commit_sequence);
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@ -1433,8 +1433,6 @@ int journal_stop(handle_t *handle)
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}
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}
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if (handle->h_sync)
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transaction->t_synchronous_commit = 1;
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current->journal_info = NULL;
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spin_lock(&journal->j_state_lock);
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spin_lock(&transaction->t_handle_lock);
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@ -479,12 +479,6 @@ struct transaction_s
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* How many handles used this transaction? [t_handle_lock]
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*/
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int t_handle_count;
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/*
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* This transaction is being forced and some process is
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* waiting for it to finish.
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*/
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unsigned int t_synchronous_commit:1;
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};
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/**
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@ -531,6 +525,8 @@ struct transaction_s
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* transaction
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* @j_commit_request: Sequence number of the most recent transaction wanting
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* commit
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* @j_commit_waited: Sequence number of the most recent transaction someone
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* is waiting for to commit.
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* @j_uuid: Uuid of client object.
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* @j_task: Pointer to the current commit thread for this journal
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* @j_max_transaction_buffers: Maximum number of metadata buffers to allow in a
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@ -695,6 +691,13 @@ struct journal_s
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*/
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tid_t j_commit_request;
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/*
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* Sequence number of the most recent transaction someone is waiting
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* for to commit.
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* [j_state_lock]
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*/
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tid_t j_commit_waited;
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/*
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* Journal uuid: identifies the object (filesystem, LVM volume etc)
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* backed by this journal. This will eventually be replaced by an array
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@ -36,19 +36,17 @@ DECLARE_EVENT_CLASS(jbd_commit,
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TP_STRUCT__entry(
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__field( dev_t, dev )
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__field( char, sync_commit )
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__field( int, transaction )
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),
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TP_fast_assign(
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__entry->dev = journal->j_fs_dev->bd_dev;
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__entry->sync_commit = commit_transaction->t_synchronous_commit;
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__entry->transaction = commit_transaction->t_tid;
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),
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TP_printk("dev %d,%d transaction %d sync %d",
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TP_printk("dev %d,%d transaction %d",
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MAJOR(__entry->dev), MINOR(__entry->dev),
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__entry->transaction, __entry->sync_commit)
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__entry->transaction)
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);
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DEFINE_EVENT(jbd_commit, jbd_start_commit,
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@ -87,19 +85,17 @@ TRACE_EVENT(jbd_drop_transaction,
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TP_STRUCT__entry(
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__field( dev_t, dev )
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__field( char, sync_commit )
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__field( int, transaction )
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),
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TP_fast_assign(
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__entry->dev = journal->j_fs_dev->bd_dev;
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__entry->sync_commit = commit_transaction->t_synchronous_commit;
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__entry->transaction = commit_transaction->t_tid;
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),
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TP_printk("dev %d,%d transaction %d sync %d",
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TP_printk("dev %d,%d transaction %d",
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MAJOR(__entry->dev), MINOR(__entry->dev),
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__entry->transaction, __entry->sync_commit)
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__entry->transaction)
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);
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TRACE_EVENT(jbd_end_commit,
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@ -109,21 +105,19 @@ TRACE_EVENT(jbd_end_commit,
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TP_STRUCT__entry(
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__field( dev_t, dev )
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__field( char, sync_commit )
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__field( int, transaction )
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__field( int, head )
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),
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TP_fast_assign(
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__entry->dev = journal->j_fs_dev->bd_dev;
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__entry->sync_commit = commit_transaction->t_synchronous_commit;
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__entry->transaction = commit_transaction->t_tid;
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__entry->head = journal->j_tail_sequence;
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),
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TP_printk("dev %d,%d transaction %d sync %d head %d",
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TP_printk("dev %d,%d transaction %d head %d",
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MAJOR(__entry->dev), MINOR(__entry->dev),
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__entry->transaction, __entry->sync_commit, __entry->head)
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__entry->transaction, __entry->head)
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);
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TRACE_EVENT(jbd_do_submit_data,
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@ -133,19 +127,17 @@ TRACE_EVENT(jbd_do_submit_data,
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TP_STRUCT__entry(
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__field( dev_t, dev )
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__field( char, sync_commit )
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__field( int, transaction )
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),
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TP_fast_assign(
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__entry->dev = journal->j_fs_dev->bd_dev;
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__entry->sync_commit = commit_transaction->t_synchronous_commit;
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__entry->transaction = commit_transaction->t_tid;
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),
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TP_printk("dev %d,%d transaction %d sync %d",
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TP_printk("dev %d,%d transaction %d",
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MAJOR(__entry->dev), MINOR(__entry->dev),
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__entry->transaction, __entry->sync_commit)
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__entry->transaction)
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);
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TRACE_EVENT(jbd_cleanup_journal_tail,
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