Re: [PATCH] xfs: don't limit software atomic writes by the group alignment

[John Garry <john.garry@linux.dev>]

On 10/1/26 17:30, Pankaj Raghav wrote:
>>
>> ----->8-----
>>
>> --- a/fs/xfs/xfs_mount.c
>> +++ b/fs/xfs/xfs_mount.c
>> @@ -694,7 +694,7 @@ xfs_calc_group_awu_max(
>>
>>          if (g->blocks == 0)
>>                  return 0;
>> -       if (btp && btp->bt_awu_min > 0)
>> +       if (btp && btp->bt_awu_max > mp->m_sb.sb_blocksize)
>>                  return max_pow_of_two_factor(g->blocks);
>>          return rounddown_pow_of_two(g->blocks);
>> }
>>
>> -----8<-----
>>
>>
>> You are advocating something like this (to solve the issue below), right?
>>
> 
> Hmm, this might fix the issue but I still don't understand why we have 
> hardware atomics check while determining SW atomics limit. Am I missing 
> something?

ok, I suppose that it (i.e. whether bt_awu_max > sb_blocksize) should 
not determine CoW-based atomics limits, but it should determine HW 
limits (in opt max).

> 
>> note: that we still need to ensure that bt_awu_min <= sb_blocksize to 
>> get HW atomics at all (so should keep a check for bt_awu_min in 
>> xfs_calc_group_awu_max() or similar)