Re: [PATCH 09/11] xfs: rework splitting of indirect block reservations

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Mar 25, 2024 at 10:24:09AM +0800, Christoph Hellwig wrote:
> Move the check if we have enough indirect blocks and the stealing of
> the deleted extent blocks out of xfs_bmap_split_indlen and into the
> caller to prepare for handling delayed allocation of RT extents that
> can't easily be stolen.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 38 ++++++++++++++++----------------------
>  1 file changed, 16 insertions(+), 22 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index cc250c33890bac..dda25a21100836 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -4829,31 +4829,17 @@ xfs_bmapi_remap(
>   * ores == 1). The number of stolen blocks is returned. The availability and
>   * subsequent accounting of stolen blocks is the responsibility of the caller.
>   */
> -static xfs_filblks_t
> +static void
>  xfs_bmap_split_indlen(
>  	xfs_filblks_t			ores,		/* original res. */
>  	xfs_filblks_t			*indlen1,	/* ext1 worst indlen */
> -	xfs_filblks_t			*indlen2,	/* ext2 worst indlen */
> -	xfs_filblks_t			avail)		/* stealable blocks */
> +	xfs_filblks_t			*indlen2)	/* ext2 worst indlen */
>  {
>  	xfs_filblks_t			len1 = *indlen1;
>  	xfs_filblks_t			len2 = *indlen2;
>  	xfs_filblks_t			nres = len1 + len2; /* new total res. */
> -	xfs_filblks_t			stolen = 0;
>  	xfs_filblks_t			resfactor;
>  
> -	/*
> -	 * Steal as many blocks as we can to try and satisfy the worst case
> -	 * indlen for both new extents.
> -	 */
> -	if (ores < nres && avail)
> -		stolen = XFS_FILBLKS_MIN(nres - ores, avail);
> -	ores += stolen;
> -
> -	 /* nothing else to do if we've satisfied the new reservation */
> -	if (ores >= nres)
> -		return stolen;
> -
>  	/*
>  	 * We can't meet the total required reservation for the two extents.
>  	 * Calculate the percent of the overall shortage between both extents
> @@ -4898,8 +4884,6 @@ xfs_bmap_split_indlen(
>  
>  	*indlen1 = len1;
>  	*indlen2 = len2;
> -
> -	return stolen;
>  }
>  
>  int
> @@ -4915,7 +4899,7 @@ xfs_bmap_del_extent_delay(
>  	struct xfs_bmbt_irec	new;
>  	int64_t			da_old, da_new, da_diff = 0;
>  	xfs_fileoff_t		del_endoff, got_endoff;
> -	xfs_filblks_t		got_indlen, new_indlen, stolen;
> +	xfs_filblks_t		got_indlen, new_indlen, stolen = 0;
>  	uint32_t		state = xfs_bmap_fork_to_state(whichfork);
>  	uint64_t		fdblocks;
>  	int			error = 0;
> @@ -4994,8 +4978,19 @@ xfs_bmap_del_extent_delay(
>  		new_indlen = xfs_bmap_worst_indlen(ip, new.br_blockcount);
>  
>  		WARN_ON_ONCE(!got_indlen || !new_indlen);
> -		stolen = xfs_bmap_split_indlen(da_old, &got_indlen, &new_indlen,
> -						       del->br_blockcount);
> +		/*
> +		 * Steal as many blocks as we can to try and satisfy the worst
> +		 * case indlen for both new extents.
> +		 */
> +		da_new = got_indlen + new_indlen;
> +		if (da_new > da_old) {
> +			stolen = XFS_FILBLKS_MIN(da_new - da_old,
> +						 new.br_blockcount);

Huh.  We used to pass del->blockcount as one of the constraints on the
stolen block count.  Why pass new.br_blockcount instead?

--D

> +			da_old += stolen;
> +		}
> +		if (da_new > da_old)
> +			xfs_bmap_split_indlen(da_old, &got_indlen, &new_indlen);
> +		da_new = got_indlen + new_indlen;
>  
>  		got->br_startblock = nullstartblock((int)got_indlen);
>  
> @@ -5007,7 +5002,6 @@ xfs_bmap_del_extent_delay(
>  		xfs_iext_next(ifp, icur);
>  		xfs_iext_insert(ip, icur, &new, state);
>  
> -		da_new = got_indlen + new_indlen - stolen;
>  		del->br_blockcount -= stolen;
>  		break;
>  	}
> -- 
> 2.39.2
>