linux-kernel - Re: [PATCH v3 09/21] xfs: Do not free EOF blocks for forcealign

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Date: Wed, 1 May 2024 09:30:37 +0100
From: John Garry <john.g.garry@...cle.com>
To: Dave Chinner <david@...morbit.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 v3 09/21] xfs: Do not free EOF blocks for forcealign

On 30/04/2024 23:54, Dave Chinner wrote:
> On Mon, Apr 29, 2024 at 05:47:34PM +0000, John Garry wrote:
>> For when forcealign is enabled, we want the EOF to be aligned as well, so
>> do not free EOF blocks.
> 
> This is doesn't match what the code does. The code is correct - it
> rounds the range to be trimmed up to the aligned offset beyond EOF
> and then frees them. The description needs to be updated to reflect
> this.

ok, fine

> 
>>
>> Signed-off-by: John Garry <john.g.garry@...cle.com>
>> ---
>>   fs/xfs/xfs_bmap_util.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
>> index 19e11d1da660..f26d1570b9bd 100644
>> --- a/fs/xfs/xfs_bmap_util.c
>> +++ b/fs/xfs/xfs_bmap_util.c
>> @@ -542,8 +542,13 @@ xfs_can_free_eofblocks(
>>   	 * forever.
>>   	 */
>>   	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)XFS_ISIZE(ip));
>> -	if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
>> +
>> +	/* Do not free blocks when forcing extent sizes */
>> +	if (xfs_inode_has_forcealign(ip) && ip->i_extsize > 1)
> 
> I see this sort of check all through the remaining patches.
> 
> Given there are significant restrictions on forced alignment,
> shouldn't this all the details be pushed inside the helper function?
> e.g.
> 
> /*
>   * Forced extent alignment is dependent on extent size hints being
>   * set to define the alignment. Alignment is only necessary when the
>   * extent size hint is larger than a single block.
>   *
>   * If reflink is enabled on the file or we are in always_cow mode,
>   * we can't easily do forced alignment.
>   *
>   * We don't support forced alignment on realtime files.
>   * XXX(dgc): why not?

There is no technical reason to not be able to support forcealign on RT, 
AFAIK. My idea is to support RT after non-RT is supported.

>   */
> static inline bool
> xfs_inode_has_forcealign(struct xfs_inode *ip)
> {
> 	if (!(ip->di_flags & XFS_DIFLAG_EXTSIZE))
> 		return false;
> 	if (ip->i_extsize <= 1)
> 		return false;
> 
> 	if (xfs_is_cow_inode(ip))
> 		return false;

Could we just include this in the forcealign validate checks? Currently 
we just check CoW extsize is zero there.

> 	if (ip->di_flags & XFS_DIFLAG_REALTIME)
> 		return false;

We check this in xfs_inode_validate_forcealign()

> 
> 	return ip->di_flags2 & XFS_DIFLAG2_FORCEALIGN;
> }
> 

So can we simply have:

static inline bool
xfs_inode_has_forcealign(struct xfs_inode *ip)
{

	if (!(ip->di_flags & XFS_DIFLAG_EXTSIZE))
		return false;
  	if (ip->i_extsize <= 1)
  		return false;
  	return ip->di_flags2 & XFS_DIFLAG2_FORCEALIGN;
}

Thanks,
John