Re: [PATCH 1/6] jbd2: optimize jbd2_journal_force_commit

[Jan Kara <jack@suse.cz>]

On Tue 28-05-13 13:18:56, Dmitry Monakhov wrote:
> Current implementation of jbd2_journal_force_commit() is suboptimal because
> result in empty and useless commits. But callers just want to force and wait
> any unfinished commits. We already has jbd2_journal_force_commit_nested()
> which does exactly what we want, except we are guaranteed that we do not hold
> journal transaction open.
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
  Hum, didn't I already review something like this?

> ---
>  fs/jbd2/journal.c     |   55 ++++++++++++++++++++++++++++++++++++------------
>  fs/jbd2/transaction.c |   23 --------------------
>  include/linux/jbd2.h  |    2 +-
>  3 files changed, 42 insertions(+), 38 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 886ec2f..078e8ea 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -566,21 +566,19 @@ int jbd2_log_start_commit(journal_t *journal, tid_t tid)
>  }
>  
>  /*
> - * Force and wait upon a commit if the calling process is not within
> - * transaction.  This is used for forcing out undo-protected data which contains
> - * bitmaps, when the fs is running out of space.
> - *
> - * We can only force the running transaction if we don't have an active handle;
> - * otherwise, we will deadlock.
> - *
> - * Returns true if a transaction was started.
> + * Force and wait any uncommitted transactions.  We can only force the running
> + * transaction if we don't have an active handle, otherwise, we will deadlock.
>   */
> -int jbd2_journal_force_commit_nested(journal_t *journal)
> +int __jbd2_journal_force_commit(journal_t *journal, int nested, int *progress)
>  {
>  	transaction_t *transaction = NULL;
>  	tid_t tid;
> -	int need_to_start = 0;
> +	int need_to_start = 0, ret = 0;
>  
> +	J_ASSERT(!current->journal_info || nested);
> +
> +	if (progress)
> +		*progress = 0;
>  	read_lock(&journal->j_state_lock);
>  	if (journal->j_running_transaction && !current->journal_info) {
>  		transaction = journal->j_running_transaction;
> @@ -590,16 +588,45 @@ int jbd2_journal_force_commit_nested(journal_t *journal)
>  		transaction = journal->j_committing_transaction;
>  
>  	if (!transaction) {
> +		/* Nothing to commit */
>  		read_unlock(&journal->j_state_lock);
> -		return 0;	/* Nothing to retry */
> +		return 0;
>  	}
> -
>  	tid = transaction->t_tid;
>  	read_unlock(&journal->j_state_lock);
>  	if (need_to_start)
>  		jbd2_log_start_commit(journal, tid);
> -	jbd2_log_wait_commit(journal, tid);
> -	return 1;
> +	ret = jbd2_log_wait_commit(journal, tid);
> +	if (!ret && progress)
> +		*progress = 1;
> +
> +	return ret;
> +}
  Can't we just make this function return <0, 0, 1 and get rid of
'progress' argument? Caller jbd2_journal_force_commit() can then return 0
if __jbd2_journal_force_commit() returned >= 0...

> +
> +/**
> + * Force and wait upon a commit if the calling process is not within
> + * transaction.  This is used for forcing out undo-protected data which contains
> + * bitmaps, when the fs is running out of space.
> + *
> + * @journal: journal to force
> + * Returns true if progress was made.
> + */
> +int jbd2_journal_force_commit_nested(journal_t *journal)
> +{
> +	int progress;
> +
> +	__jbd2_journal_force_commit(journal, 1, &progress);
> +	return progress;
> +}
> +
> +/**
> + * int journal_force_commit() - force any uncommitted transactions
> + * @journal: journal to force
> + *
> + */
> +int jbd2_journal_force_commit(journal_t *journal)
> +{
> +	return __jbd2_journal_force_commit(journal, 0, NULL);
>  }
  Also if we move the WARN_ON(!current->journal_info) here, we can remove
the 'nested' argument.

								Honza

>  /*
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 10f524c..dae6b3d 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1522,29 +1522,6 @@ int jbd2_journal_stop(handle_t *handle)
>  	return err;
>  }
>  
> -/**
> - * int jbd2_journal_force_commit() - force any uncommitted transactions
> - * @journal: journal to force
> - *
> - * For synchronous operations: force any uncommitted transactions
> - * to disk.  May seem kludgy, but it reuses all the handle batching
> - * code in a very simple manner.
> - */
> -int jbd2_journal_force_commit(journal_t *journal)
> -{
> -	handle_t *handle;
> -	int ret;
> -
> -	handle = jbd2_journal_start(journal, 1);
> -	if (IS_ERR(handle)) {
> -		ret = PTR_ERR(handle);
> -	} else {
> -		handle->h_sync = 1;
> -		ret = jbd2_journal_stop(handle);
> -	}
> -	return ret;
> -}
> -
>  /*
>   *
>   * List management code snippets: various functions for manipulating the
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 6e051f4..c9e1ab6 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1125,6 +1125,7 @@ extern void	   jbd2_journal_ack_err    (journal_t *);
>  extern int	   jbd2_journal_clear_err  (journal_t *);
>  extern int	   jbd2_journal_bmap(journal_t *, unsigned long, unsigned long long *);
>  extern int	   jbd2_journal_force_commit(journal_t *);
> +extern int	   jbd2_journal_force_commit_nested(journal_t *);
>  extern int	   jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *inode);
>  extern int	   jbd2_journal_begin_ordered_truncate(journal_t *journal,
>  				struct jbd2_inode *inode, loff_t new_size);
> @@ -1199,7 +1200,6 @@ int __jbd2_log_space_left(journal_t *); /* Called with journal locked */
>  int jbd2_log_start_commit(journal_t *journal, tid_t tid);
>  int __jbd2_log_start_commit(journal_t *journal, tid_t tid);
>  int jbd2_journal_start_commit(journal_t *journal, tid_t *tid);
> -int jbd2_journal_force_commit_nested(journal_t *journal);
>  int jbd2_log_wait_commit(journal_t *journal, tid_t tid);
>  int jbd2_complete_transaction(journal_t *journal, tid_t tid);
>  int jbd2_log_do_checkpoint(journal_t *journal);
> -- 
> 1.7.1
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR