Re: [PATCH 12/14] xfs: merge xlog_state_set_callback into xlog_state_iodone_process_iclog

[Brian Foster <bfoster@redhat.com>]

On Mon, Mar 16, 2020 at 03:42:31PM +0100, Christoph Hellwig wrote:
> Merge xlog_state_set_callback into its only caller, which makes the iclog
> I/O completion handling a little easier to follow.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  fs/xfs/xfs_log.c | 74 +++++++++++++++++++++---------------------------
>  1 file changed, 33 insertions(+), 41 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 899c324d07e2..865dd1e08679 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2645,46 +2645,6 @@ xlog_get_lowest_lsn(
>  	return lowest_lsn;
>  }
>  
> -/*
> - * Completion of a iclog IO does not imply that a transaction has completed, as
> - * transactions can be large enough to span many iclogs. We cannot change the
> - * tail of the log half way through a transaction as this may be the only
> - * transaction in the log and moving the tail to point to the middle of it
> - * will prevent recovery from finding the start of the transaction. Hence we
> - * should only update the last_sync_lsn if this iclog contains transaction
> - * completion callbacks on it.
> - *
> - * We have to do this before we drop the icloglock to ensure we are the only one
> - * that can update it.
> - *
> - * If we are moving the last_sync_lsn forwards, we also need to ensure we kick
> - * the reservation grant head pushing. This is due to the fact that the push
> - * target is bound by the current last_sync_lsn value. Hence if we have a large
> - * amount of log space bound up in this committing transaction then the
> - * last_sync_lsn value may be the limiting factor preventing tail pushing from
> - * freeing space in the log. Hence once we've updated the last_sync_lsn we
> - * should push the AIL to ensure the push target (and hence the grant head) is
> - * no longer bound by the old log head location and can move forwards and make
> - * progress again.
> - */
> -static void
> -xlog_state_set_callback(
> -	struct xlog		*log,
> -	struct xlog_in_core	*iclog,
> -	xfs_lsn_t		header_lsn)
> -{
> -	iclog->ic_state = XLOG_STATE_CALLBACK;
> -
> -	ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
> -			   header_lsn) <= 0);
> -
> -	if (list_empty_careful(&iclog->ic_callbacks))
> -		return;
> -
> -	atomic64_set(&log->l_last_sync_lsn, header_lsn);
> -	xlog_grant_push_ail(log, 0);
> -}
> -
>  /*
>   * Keep processing entries in the iclog callback list until we come around and
>   * it is empty.  We need to atomically see that the list is empty and change the
> @@ -2741,7 +2701,39 @@ xlog_state_iodone_process_iclog(
>  	if (lowest_lsn && XFS_LSN_CMP(lowest_lsn, header_lsn) < 0)
>  		return false;
>  
> -	xlog_state_set_callback(log, iclog, header_lsn);
> +	iclog->ic_state = XLOG_STATE_CALLBACK;
> +
> +	ASSERT(XFS_LSN_CMP(atomic64_read(&log->l_last_sync_lsn),
> +			   header_lsn) <= 0);
> +
> +	/*
> +	 * Completion of an iclog I/O does not imply that a transaction has
> +	 * completed, as transactions can be large enough to span multiple
> +	 * iclogs.  We cannot change the tail of the log half way through a
> +	 * transaction as this may be the only transaction in the log and moving
> +	 * the tail to point to the middle of it will prevent recovery from
> +	 * finding the start of the transaction. Hence we should only update
> +	 * the last_sync_lsn if this iclog contains transaction completion
> +	 * callbacks on it.
> +	 *
> +	 * We have to do this before we drop the icloglock to ensure we are the
> +	 * only one that can update it.
> +	 *
> +	 * If we are moving last_sync_lsn forwards, we also need to ensure we
> +	 * kick the reservation grant head pushing. This is due to the fact that
> +	 * the push target is bound by the current last_sync_lsn value.  If we
> +	 * have a large amount of log space bound up in this committing
> +	 * transaction then the last_sync_lsn value may be the limiting factor
> +	 * preventing tail pushing from freeing space in the log.  Hence once
> +	 * we've updated the last_sync_lsn we should push the AIL to ensure the
> +	 * push target (and hence the grant head) is no longer bound by the old
> +	 * log head location and can move forwards and make progress again.
> +	 */
> +	if (!list_empty_careful(&iclog->ic_callbacks)) {
> +		atomic64_set(&log->l_last_sync_lsn, header_lsn);
> +		xlog_grant_push_ail(log, 0);
> +	}
> +
>  	xlog_state_do_iclog_callbacks(log, iclog);
>  
>  	iclog->ic_state = XLOG_STATE_DIRTY;
> -- 
> 2.24.1
>