linux-kernel - Re: [PATCH RFC v3 11/21] xfs: Unmap blocks according to forcealign

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Message-ID: <ZjGIktQV12qas14f@dread.disaster.area>
Date: Wed, 1 May 2024 10:10:58 +1000
From: Dave Chinner <david@...morbit.com>
To: John Garry <john.g.garry@...cle.com>
Cc: djwong@...nel.org, hch@....de, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, chandan.babu@...cle.com,
	willy@...radead.org, axboe@...nel.dk, martin.petersen@...cle.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@....edu, jbongio@...gle.com, ojaswin@...ux.ibm.com,
	ritesh.list@...il.com, mcgrof@...nel.org, p.raghav@...sung.com,
	linux-xfs@...r.kernel.org, catherine.hoang@...cle.com
Subject: Re: [PATCH RFC v3 11/21] xfs: Unmap blocks according to forcealign

On Mon, Apr 29, 2024 at 05:47:36PM +0000, John Garry wrote:
> For when forcealign is enabled, blocks in an inode need to be unmapped
> according to extent alignment, like what is already done for rtvol.
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 39 +++++++++++++++++++++++++++++++++------
>  fs/xfs/xfs_inode.h       |  5 +++++
>  2 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 4f39a43d78a7..4a78ab193753 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5339,6 +5339,15 @@ xfs_bmap_del_extent_real(
>  	return 0;
>  }
>  
> +/* Return the offset of an block number within an extent for forcealign. */
> +static xfs_extlen_t
> +xfs_forcealign_extent_offset(
> +	struct xfs_inode	*ip,
> +	xfs_fsblock_t		bno)
> +{
> +	return bno & (ip->i_extsize - 1);
> +}
> +
>  /*
>   * Unmap (remove) blocks from a file.
>   * If nexts is nonzero then the number of extents to remove is limited to
> @@ -5361,6 +5370,7 @@ __xfs_bunmapi(
>  	struct xfs_bmbt_irec	got;		/* current extent record */
>  	struct xfs_ifork	*ifp;		/* inode fork pointer */
>  	int			isrt;		/* freeing in rt area */
> +	int			isforcealign;	/* freeing for file inode with forcealign */
>  	int			logflags;	/* transaction logging flags */
>  	xfs_extlen_t		mod;		/* rt extent offset */
>  	struct xfs_mount	*mp = ip->i_mount;
> @@ -5397,7 +5407,10 @@ __xfs_bunmapi(
>  		return 0;
>  	}
>  	XFS_STATS_INC(mp, xs_blk_unmap);
> -	isrt = xfs_ifork_is_realtime(ip, whichfork);
> +	isrt = (whichfork == XFS_DATA_FORK) && XFS_IS_REALTIME_INODE(ip);

Why did you change this check? What's wrong with
xfs_ifork_is_realtime(), and if there is something wrong, why
shouldn't xfs_ifork_is_relatime() get fixed?

> +	isforcealign = (whichfork == XFS_DATA_FORK) &&
> +			xfs_inode_has_forcealign(ip) &&
> +			xfs_inode_has_extsize(ip) && ip->i_extsize > 1;

This is one of the reasons why I said xfs_inode_has_forcealign()
should be checking that extent size hints should be checked in that
helper....

>  	end = start + len;
>  
>  	if (!xfs_iext_lookup_extent_before(ip, ifp, &end, &icur, &got)) {
> @@ -5459,11 +5472,15 @@ __xfs_bunmapi(
>  		if (del.br_startoff + del.br_blockcount > end + 1)
>  			del.br_blockcount = end + 1 - del.br_startoff;
>  
> -		if (!isrt || (flags & XFS_BMAPI_REMAP))
> +		if ((!isrt && !isforcealign) || (flags & XFS_BMAPI_REMAP))
>  			goto delete;
>  
> -		mod = xfs_rtb_to_rtxoff(mp,
> -				del.br_startblock + del.br_blockcount);
> +		if (isrt)
> +			mod = xfs_rtb_to_rtxoff(mp,
> +					del.br_startblock + del.br_blockcount);
> +		else if (isforcealign)
> +			mod = xfs_forcealign_extent_offset(ip,
> +					del.br_startblock + del.br_blockcount);

There's got to be a cleaner way to do this.

We already know that either isrt or isforcealign must be set here,
so there's no need for the "else if" construct.

Also, forcealign should take precedence over realtime, so that
forcealign will work on realtime devices as well. I'd change this
code to call a wrapper like:

		mod = xfs_bunmapi_align(ip, del.br_startblock + del.br_blockcount);

static xfs_extlen_t
xfs_bunmapi_align(
	struct xfs_inode	*ip,
	xfs_fsblock_t		bno)
{
	if (!XFS_INODE_IS_REALTIME(ip)) {
		ASSERT(xfs_inode_has_forcealign(ip))
		if (is_power_of_2(ip->i_extsize))
			return bno & (ip->i_extsize - 1);
		return do_div(bno, ip->i_extsize);
	}
	return xfs_rtb_to_rtxoff(ip->i_mount, bno);
}



>  		if (mod) {
>  			/*
>  			 * Realtime extent not lined up at the end.
> @@ -5511,9 +5528,19 @@ __xfs_bunmapi(
>  			goto nodelete;
>  		}
>  
> -		mod = xfs_rtb_to_rtxoff(mp, del.br_startblock);
> +		if (isrt)
> +			mod = xfs_rtb_to_rtxoff(mp, del.br_startblock);
> +		else if (isforcealign)
> +			mod = xfs_forcealign_extent_offset(ip,
> +					del.br_startblock);
> +
		mod = xfs_bunmapi_align(ip, del.br_startblock);

>  		if (mod) {
> -			xfs_extlen_t off = mp->m_sb.sb_rextsize - mod;
> +			xfs_extlen_t off;
> +
> +			if (isrt)
> +				off = mp->m_sb.sb_rextsize - mod;
> +			else if (isforcealign)
> +				off = ip->i_extsize - mod;

			if (forcealign)
				off = ip->i_extsize - mod;
			else
				off = mp->m_sb.sb_rextsize - mod;

-Dave.
-- 
Dave Chinner
david@...morbit.com