Re: [PATCH 06/14] xfs: reset dfops to initial state after finish

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jul 19, 2018 at 09:49:11AM -0400, Brian Foster wrote:
> xfs_defer_init() is currently used in two particular situations. The
> first and most obvious case is raw initialization of an
> xfs_defer_ops struct. The other case is partial reinit of
> xfs_defer_ops on reuse due to iteration.
> 
> Most instances of the first case will be replaced by a single init
> of a dfops embedded in the transaction. Init calls are still
> technically required for the second case because the dfops may have
> low space mode enabled or have joined items that need to be reset
> before the dfops should be reused.
> 
> Since the current dfops usage expects either a final transaction
> commit after xfs_defer_finish() or xfs_defer_init() if dfops is to
> be reused, we can shift some of the init logic into
> xfs_defer_finish() such that the latter returns with a reinitialized
> dfops. This eliminates the second dependency noted above such that a
> dfops is immediately ready for reuse after an xfs_defer_finish()
> without the need to change any calling code.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
>  fs/xfs/libxfs/xfs_defer.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> index d3466087db16..e6baa27a690b 100644
> --- a/fs/xfs/libxfs/xfs_defer.c
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -319,6 +319,29 @@ xfs_defer_bjoin(
>  	return -EFSCORRUPTED;
>  }
>  
> +/*
> + * Reset an already used dfops after finish.
> + */
> +static void
> +xfs_defer_reset(
> +	struct xfs_defer_ops	*dop)
> +{
> +	int 			i;
> +
> +	ASSERT(!xfs_defer_has_unfinished_work(dop));
> +	dop->dop_low = false;
> +	for (i = 0; i < XFS_DEFER_OPS_NR_INODES; i++) {
> +		if (!dop->dop_inodes[i])
> +			break;
> +		dop->dop_inodes[i] = NULL;
> +	}
> +	for (i = 0; i < XFS_DEFER_OPS_NR_BUFS; i++) {
> +		if (!dop->dop_bufs[i])
> +			break;
> +		dop->dop_bufs[i] = NULL;
> +	}
> +}

Are these loops really more efficient than just doing memsets
of dop_inodes and dop_bufs?

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>