Re: [PATCH 5/5] xfs: xfs_defer_capture should absorb remaining transaction reservation

[Brian Foster <bfoster@redhat.com>]

On Tue, Sep 29, 2020 at 10:43:44AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When xfs_defer_capture extracts the deferred ops and transaction state
> from a transaction, it should record the transaction reservation type
> from the old transaction so that when we continue the dfops chain, we
> still use the same reservation parameters.
> 
> Doing this means that the log item recovery functions get to determine
> the transaction reservation instead of abusing tr_itruncate in yet
> another part of xfs.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---

Much nicer, and FWIW this is pretty much the approach I was wondering
about wrt to the block reservation in the previous patch..

>  fs/xfs/libxfs/xfs_defer.c |    9 +++++++++
>  fs/xfs/libxfs/xfs_defer.h |    1 +
>  fs/xfs/xfs_log_recover.c  |    4 ++--
>  3 files changed, 12 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
> index 0cceebb390c4..4caaf5527403 100644
> --- a/fs/xfs/libxfs/xfs_defer.c
> +++ b/fs/xfs/libxfs/xfs_defer.c
> @@ -579,6 +579,15 @@ xfs_defer_ops_capture(
>  	dfc->dfc_blkres = tp->t_blk_res - tp->t_blk_res_used;
>  	tp->t_blk_res = tp->t_blk_res_used;
>  
> +	/*
> +	 * Preserve the transaction reservation type.  The logcount is
> +	 * hardwired to 1 to so that we can make forward progress in recovery
> +	 * no matter how full the log might be, at a cost of more regrants.
> +	 */
> +	dfc->dfc_tres.tr_logres = tp->t_log_res;
> +	dfc->dfc_tres.tr_logcount = 1;
> +	dfc->dfc_tres.tr_logflags = XFS_TRANS_PERM_LOG_RES;

Any real need to allocate these last two fields in every captured chain
when they're basically hardcoded? If not, it might be a bit more
efficient to put an xfs_trans_res on the stack in
xlog_finish_defer_ops() and just save the logres value here.

Brian

> +
>  	return dfc;
>  }
>  
> diff --git a/fs/xfs/libxfs/xfs_defer.h b/fs/xfs/libxfs/xfs_defer.h
> index b1c7b761afd5..c447c79bbe74 100644
> --- a/fs/xfs/libxfs/xfs_defer.h
> +++ b/fs/xfs/libxfs/xfs_defer.h
> @@ -76,6 +76,7 @@ struct xfs_defer_capture {
>  	struct list_head	dfc_dfops;
>  	unsigned int		dfc_tpflags;
>  	unsigned int		dfc_blkres;
> +	struct xfs_trans_res	dfc_tres;
>  };
>  
>  /*
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index b06c9881a13d..46e750279634 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -2442,8 +2442,8 @@ xlog_finish_defer_ops(
>  	int			error = 0;
>  
>  	list_for_each_entry_safe(dfc, next, capture_list, dfc_list) {
> -		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0,
> -				0, XFS_TRANS_RESERVE, &tp);
> +		error = xfs_trans_alloc(mp, &dfc->dfc_tres, 0, 0,
> +				XFS_TRANS_RESERVE, &tp);
>  		if (error)
>  			return error;
>  
>