Re: [PATCH 27/45] xfs: pass lv chain length into xlog_write()

[Brian Foster <bfoster@redhat.com>]

On Fri, Mar 05, 2021 at 04:11:25PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> The caller of xlog_write() usually has a close accounting of the
> aggregated vector length contained in the log vector chain passed to
> xlog_write(). There is no need to iterate the chain to calculate he
> length of the data in xlog_write_calculate_len() if the caller is
> already iterating that chain to build it.
> 
> Passing in the vector length avoids doing an extra chain iteration,
> which can be a significant amount of work given that large CIL
> commits can have hundreds of thousands of vectors attached to the
> chain.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_log.c      | 37 ++++++-------------------------------
>  fs/xfs/xfs_log_cil.c  | 18 +++++++++++++-----
>  fs/xfs/xfs_log_priv.h |  2 +-
>  3 files changed, 20 insertions(+), 37 deletions(-)
> 
...
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 7a5e6bdb7876..34abc3bae587 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
...
> @@ -893,6 +898,9 @@ xlog_cil_push_work(
>  	 * transaction header here as it is not accounted for in xlog_write().
>  	 */
>  	xlog_cil_build_trans_hdr(ctx, &thdr, &lvhdr, num_iovecs);
> +	num_iovecs += lvhdr.lv_niovecs;

What's the point of this if num_iovecs is only used by
xlog_cil_build_trans_hdr()?

Brian

> +	num_bytes += lvhdr.lv_bytes;
> +
>  
>  	/*
>  	 * Before we format and submit the first iclog, we have to ensure that
> @@ -907,7 +915,7 @@ xlog_cil_push_work(
>  	 * write head.
>  	 */
>  	error = xlog_write(log, &lvhdr, ctx->ticket, &ctx->start_lsn, NULL,
> -				XLOG_START_TRANS);
> +				XLOG_START_TRANS, num_bytes);
>  	if (error)
>  		goto out_abort_free_ticket;
>  
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 8ee6a5f74396..003c11653955 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -462,7 +462,7 @@ void	xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
>  void	xlog_print_trans(struct xfs_trans *);
>  int	xlog_write(struct xlog *log, struct xfs_log_vec *log_vector,
>  		struct xlog_ticket *tic, xfs_lsn_t *start_lsn,
> -		struct xlog_in_core **commit_iclog, uint optype);
> +		struct xlog_in_core **commit_iclog, uint optype, uint32_t len);
>  int	xlog_commit_record(struct xlog *log, struct xlog_ticket *ticket,
>  		struct xlog_in_core **iclog, xfs_lsn_t *lsn);
>  void	xlog_state_switch_iclogs(struct xlog *log, struct xlog_in_core *iclog,
> -- 
> 2.28.0
>