Re: [PATCH 09/29] jbd2: Cleanup needed free block estimates when starting a transaction

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Mon, Apr 08, 2013 at 11:32:14PM +0200, Jan Kara wrote:
> __jbd2_log_space_left() and jbd_space_needed() were kind of odd.
> jbd_space_needed() accounted also credits needed for currently committing
> transaction while it didn't account for credits needed for control blocks.
> __jbd2_log_space_left() then accounted for control blocks as a fraction of free
> space. Since results of these two functions are always only compared against
> each other, this works correct but is somewhat strange. Move the estimates so
> that jbd_space_needed() returns number of blocks needed for a transaction
> including control blocks and __jbd2_log_space_left() returns free space in the
> journal (with the committing transaction already subtracted). Rename functions
> to jbd2_log_space_left() and jbd2_space_needed() while we are changing them.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>
Regards,
                                                - Zheng

> ---
>  fs/jbd2/checkpoint.c  |    8 ++++----
>  fs/jbd2/journal.c     |   29 -----------------------------
>  fs/jbd2/transaction.c |    9 +++++----
>  include/linux/jbd2.h  |   32 ++++++++++++++++++++++++++------
>  4 files changed, 35 insertions(+), 43 deletions(-)
> 
> diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
> index 65ec076..a572383 100644
> --- a/fs/jbd2/checkpoint.c
> +++ b/fs/jbd2/checkpoint.c
> @@ -120,8 +120,8 @@ void __jbd2_log_wait_for_space(journal_t *journal)
>  	int nblocks, space_left;
>  	/* assert_spin_locked(&journal->j_state_lock); */
>  
> -	nblocks = jbd_space_needed(journal);
> -	while (__jbd2_log_space_left(journal) < nblocks) {
> +	nblocks = jbd2_space_needed(journal);
> +	while (jbd2_log_space_left(journal) < nblocks) {
>  		if (journal->j_flags & JBD2_ABORT)
>  			return;
>  		write_unlock(&journal->j_state_lock);
> @@ -140,8 +140,8 @@ void __jbd2_log_wait_for_space(journal_t *journal)
>  		 */
>  		write_lock(&journal->j_state_lock);
>  		spin_lock(&journal->j_list_lock);
> -		nblocks = jbd_space_needed(journal);
> -		space_left = __jbd2_log_space_left(journal);
> +		nblocks = jbd2_space_needed(journal);
> +		space_left = jbd2_log_space_left(journal);
>  		if (space_left < nblocks) {
>  			int chkpt = journal->j_checkpoint_transactions != NULL;
>  			tid_t tid = 0;
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index e9a9cdb..e6f14e0 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -480,35 +480,6 @@ repeat:
>   */
>  
>  /*
> - * __jbd2_log_space_left: Return the number of free blocks left in the journal.
> - *
> - * Called with the journal already locked.
> - *
> - * Called under j_state_lock
> - */
> -
> -int __jbd2_log_space_left(journal_t *journal)
> -{
> -	int left = journal->j_free;
> -
> -	/* assert_spin_locked(&journal->j_state_lock); */
> -
> -	/*
> -	 * Be pessimistic here about the number of those free blocks which
> -	 * might be required for log descriptor control blocks.
> -	 */
> -
> -#define MIN_LOG_RESERVED_BLOCKS 32 /* Allow for rounding errors */
> -
> -	left -= MIN_LOG_RESERVED_BLOCKS;
> -
> -	if (left <= 0)
> -		return 0;
> -	left -= (left >> 3);
> -	return left;
> -}
> -
> -/*
>   * Called with j_state_lock locked for writing.
>   * Returns true if a transaction commit was started.
>   */
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 74cfbd3..aee40c9 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -283,12 +283,12 @@ repeat:
>  	 * reduce the free space arbitrarily.  Be careful to account for
>  	 * those buffers when checkpointing.
>  	 */
> -	if (__jbd2_log_space_left(journal) < jbd_space_needed(journal)) {
> +	if (jbd2_log_space_left(journal) < jbd2_space_needed(journal)) {
>  		jbd_debug(2, "Handle %p waiting for checkpoint...\n", handle);
>  		atomic_sub(nblocks, &transaction->t_outstanding_credits);
>  		read_unlock(&journal->j_state_lock);
>  		write_lock(&journal->j_state_lock);
> -		if (__jbd2_log_space_left(journal) < jbd_space_needed(journal))
> +		if (jbd2_log_space_left(journal) < jbd2_space_needed(journal))
>  			__jbd2_log_wait_for_space(journal);
>  		write_unlock(&journal->j_state_lock);
>  		goto repeat;
> @@ -306,7 +306,7 @@ repeat:
>  	jbd_debug(4, "Handle %p given %d credits (total %d, free %d)\n",
>  		  handle, nblocks,
>  		  atomic_read(&transaction->t_outstanding_credits),
> -		  __jbd2_log_space_left(journal));
> +		  jbd2_log_space_left(journal));
>  	read_unlock(&journal->j_state_lock);
>  
>  	lock_map_acquire(&handle->h_lockdep_map);
> @@ -442,7 +442,8 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
>  		goto unlock;
>  	}
>  
> -	if (wanted > __jbd2_log_space_left(journal)) {
> +	if (wanted + (wanted >> JBD2_CONTROL_BLOCKS_SHIFT) >
> +	    jbd2_log_space_left(journal)) {
>  		jbd_debug(3, "denied handle %p %d blocks: "
>  			  "insufficient log space\n", handle, nblocks);
>  		goto unlock;
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index be5115f..9197d1b 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1219,7 +1219,6 @@ extern void	jbd2_clear_buffer_revoked_flags(journal_t *journal);
>   * transitions on demand.
>   */
>  
> -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);
> @@ -1289,16 +1288,37 @@ extern int jbd2_journal_blocks_per_page(struct inode *inode);
>  extern size_t journal_tag_bytes(journal_t *journal);
>  
>  /*
> + * We reserve t_outstanding_credits >> JBD2_CONTROL_BLOCKS_SHIFT for
> + * transaction control blocks.
> + */
> +#define JBD2_CONTROL_BLOCKS_SHIFT 5
> +
> +/*
>   * Return the minimum number of blocks which must be free in the journal
>   * before a new transaction may be started.  Must be called under j_state_lock.
>   */
> -static inline int jbd_space_needed(journal_t *journal)
> +static inline int jbd2_space_needed(journal_t *journal)
>  {
>  	int nblocks = journal->j_max_transaction_buffers;
> -	if (journal->j_committing_transaction)
> -		nblocks += atomic_read(&journal->j_committing_transaction->
> -				       t_outstanding_credits);
> -	return nblocks;
> +	return nblocks + (nblocks >> JBD2_CONTROL_BLOCKS_SHIFT);
> +}
> +
> +/*
> + * Return number of free blocks in the log. Must be called under j_state_lock.
> + */
> +static inline unsigned long jbd2_log_space_left(journal_t *journal)
> +{
> +	/* Allow for rounding errors */
> +	unsigned long free = journal->j_free - 32;
> +
> +	if (journal->j_committing_transaction) {
> +		unsigned long committing = atomic_read(&journal->
> +			j_committing_transaction->t_outstanding_credits);
> +
> +		/* Transaction + control blocks */
> +		free -= committing + (committing >> JBD2_CONTROL_BLOCKS_SHIFT);
> +	}
> +	return free;
>  }
>  
>  /*
> -- 
> 1.7.1
> 
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