Re: [PATCH v2] jbd2: speed up jbd2_transaction_committed()

[Jan Kara]

On Mon 20-05-24 21:18:31, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> jbd2_transaction_committed() is used to check whether a transaction with
> the given tid has already committed, it holds j_state_lock in read mode
> and check the tid of current running transaction and committing
> transaction, but holding the j_state_lock is expensive.
> 
> We have already stored the sequence number of the most recently
> committed transaction in journal t->j_commit_sequence, we could do this
> check by comparing it with the given tid instead. If the given tid isn't
> smaller than j_commit_sequence, we can ensure that the given transaction
> has been committed. That way we could drop the expensive lock and
> achieve about 10% ~ 20% performance gains in concurrent DIOs on may
> virtual machine with 100G ramdisk.
> 
> fio -filename=/mnt/foo -direct=1 -iodepth=10 -rw=$rw -ioengine=libaio \
>     -bs=4k -size=10G -numjobs=10 -runtime=60 -overwrite=1 -name=test \
>     -group_reporting
> 
> Before:
>   overwrite       IOPS=88.2k, BW=344MiB/s
>   read            IOPS=95.7k, BW=374MiB/s
>   rand overwrite  IOPS=98.7k, BW=386MiB/s
>   randread        IOPS=102k, BW=397MiB/s
> 
> After:
>   overwrite       IOPS=105k, BW=410MiB/s
>   read            IOPS=112k, BW=436MiB/s
>   rand overwrite  IOPS=104k, BW=404MiB/s
>   randread        IOPS=111k, BW=432MiB/s
> 
> CC: Dave Chinner <david@xxxxxxxxxxxxx>
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/linux-ext4/ZjILCPNZRHeazSqV@xxxxxxxxxxxxxxxxxxx/
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

Thanks! The patch looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
> v1->v2:
>  - Add READ_ONCE and WRITE_ONCE to access ->j_commit_sequence
>    concurrently.
>  - Keep the jbd2_transaction_committed() helper.
> 
>  fs/jbd2/commit.c  |  2 +-
>  fs/jbd2/journal.c | 12 +-----------
>  2 files changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 5e122586e06e..8244cab17688 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -1108,7 +1108,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>  
>  	commit_transaction->t_state = T_COMMIT_CALLBACK;
>  	J_ASSERT(commit_transaction == journal->j_committing_transaction);
> -	journal->j_commit_sequence = commit_transaction->t_tid;
> +	WRITE_ONCE(journal->j_commit_sequence, commit_transaction->t_tid);
>  	journal->j_committing_transaction = NULL;
>  	commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
>  
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index b6c114c11b97..cc586e3c4ee1 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -789,17 +789,7 @@ EXPORT_SYMBOL(jbd2_fc_end_commit_fallback);
>  /* Return 1 when transaction with given tid has already committed. */
>  int jbd2_transaction_committed(journal_t *journal, tid_t tid)
>  {
> -	int ret = 1;
> -
> -	read_lock(&journal->j_state_lock);
> -	if (journal->j_running_transaction &&
> -	    journal->j_running_transaction->t_tid == tid)
> -		ret = 0;
> -	if (journal->j_committing_transaction &&
> -	    journal->j_committing_transaction->t_tid == tid)
> -		ret = 0;
> -	read_unlock(&journal->j_state_lock);
> -	return ret;
> +	return tid_geq(READ_ONCE(journal->j_commit_sequence), tid);
>  }
>  EXPORT_SYMBOL(jbd2_transaction_committed);
>  
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR