Re: [PATCH v2 06/14] fs: xfs: Do not free EOF blocks for forcealign

John Garry
2024-03-07T11:40:14Z

>> */
>> 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 */
>
> That comment seems wrong - this just rounds up where we start
> trimming from to be aligned...

ok

>
>> + if (xfs_get_extsz(ip) > 1)
>> + end_fsb = roundup_64(end_fsb, xfs_get_extsz(ip));
>> + else if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
>> end_fsb = xfs_rtb_roundup_rtx(mp, end_fsb);
>
> I think this would be better written as:
>
> /*
> * Forced extent alignment requires us to round up where we
> * start trimming from so that result is correctly aligned.
> */
> if (xfs_inode_forcealign(ip)) {
> if (ip->i_extsize > 1)
> end_fsb = roundup_64(end_fsb, ip->i_extsize);
> else if (XFS_IS_REALTIME_INODE(ip) && mp->m_sb.sb_rextsize > 1)
> end_fsb = xfs_rtb_roundup_rtx(mp, end_fsb);
> }
>
> Because we only want end-fsb alignment when forced alignment is
> required.

But why change current rtvol behaviour?

>
> Which then makes me wonder: truncate needs this, too, doesn't it?
> And the various fallocate() ops like hole punching and extent
> shifting?
>

Yes, I would think so. I quickly checked rtvol for truncate and it does
the round up. I would need to check the relevant code for truncate and
fallocate for forcealign now.

I do also wonder if we could factor out this rounding up code for
truncate, facallocate, and whatever else.

>> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
>> index 2c439df8c47f..bbb8886f1d32 100644
>> --- a/fs/xfs/xfs_inode.c
>> +++ b/fs/xfs/xfs_inode.c
>> @@ -65,6 +65,20 @@ xfs_get_extsz_hint(
>> return 0;
>> }
>>
>> +/*
>> + * Helper function to extract extent size. It will return a power-of-2,
>> + * as forcealign requires this.
>> + */
>> +xfs_extlen_t
>> +xfs_get_extsz(
>> + struct xfs_inode *ip)
>> +{
>> + if (xfs_inode_forcealign(ip) && ip->i_extsize)
>> + return ip->i_extsize;
>> +
>> + return 1;
>> +}
>
> This can go away - if it is needed elsewhere, then I think it would
> be better open coded because it better documents what the code is
> doing...
>

I would rather get rid of xfs_get_extsz() for sure.

Thanks,
John