Re: [PATCH 12/15] xfs: replace xfs_defer_ops ->dop_pending with on-stack list

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jul 30, 2018 at 12:45:17PM -0400, Brian Foster wrote:
> The xfs_defer_ops ->dop_pending list is used to track active
> deferred operations once intents are logged. These items must be
> aborted in the event of an error. The list is populated as intents
> are logged and items are removed as they complete (or are aborted).
> 
> Now that xfs_defer_finish() cancels on error, there is no need to
> ever access ->dop_pending outside of xfs_defer_finish(). The list is
> only ever populated after xfs_defer_finish() begins and is either
> completed or cancelled before it returns.
> 
> Remove ->dop_pending from xfs_defer_ops and replace it with a local
> list in the xfs_defer_finish() path. Pass the local list to the
> various helpers now that it is not accessible via dfops. Note that
> we have to check for NULL in the abort case as the final tx roll
> occurs outside of the scope of the new local list (once the dfops
> has completed and thus drained the list).
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_defer.c | 80 ++++++++++++++++++++-------------------
>  fs/xfs/libxfs/xfs_defer.h |  3 +-
>  fs/xfs/xfs_trace.h        |  1 -
>  fs/xfs/xfs_trans.h        |  1 -
>  4 files changed, 43 insertions(+), 42 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> index 66848ede62c0..6bf792e2d61b 100644
> --- a/fs/xfs/libxfs/xfs_defer.c
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -174,6 +174,8 @@
>  
>  static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX];
>  
> +static void __xfs_defer_cancel(struct list_head *);

Can you just move __xfs_defer_cancel up to here to avoid the
forward declaration?

> +
>  /*
>   * For each pending item in the intake list, log its intent item and the
>   * associated extents, then add the entire intake list to the end of
> @@ -181,7 +183,8 @@ static const struct xfs_defer_op_type *defer_op_types[XFS_DEFER_OPS_TYPE_MAX];
>   */
>  STATIC void
>  xfs_defer_intake_work(
> -	struct xfs_trans		*tp)
> +	struct xfs_trans		*tp,
> +	struct list_head		*dop_pending)
>  {
>  	struct xfs_defer_ops		*dop = tp->t_dfops;
>  	struct list_head		*li;
> @@ -197,13 +200,14 @@ xfs_defer_intake_work(
>  			dfp->dfp_type->log_item(tp, dfp->dfp_intent, li);
>  	}
>  
> -	list_splice_tail_init(&dop->dop_intake, &dop->dop_pending);
> +	list_splice_tail_init(&dop->dop_intake, dop_pending);

It almost seems simpler to just move the list_splice_tail_init to the
(only) caller.

> @@ -292,9 +299,10 @@ xfs_defer_trans_roll(
>  /* Do we have any work items to finish? */
>  bool
>  xfs_defer_has_unfinished_work(
> -	struct xfs_trans		*tp)
> +	struct xfs_trans		*tp,
> +	struct list_head		*dop_pending)
>  {
> -	return !list_empty(&tp->t_dfops->dop_pending) ||
> +	return !list_empty(dop_pending) ||
>  		!list_empty(&tp->t_dfops->dop_intake);
>  }

I'd just opencode this in the only caller that is left.