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

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

On 9/30/26 06:10, Pankaj Raghav (Samsung) wrote:
>>> Just to give more context:
>>>
>>> Trace of calc_atomic_write_unit_max:
>>>
>>>    mount-696   [010]   449.230543: xfs_calc_atomic_write_unit_max: dev
>>> 259:0 ag max_write 262144 max_ioend 512 max_gsize 134217728 awu_max 512
>>>
>>> 2097152 comes from awumax being 512 fsblocks.
>>>
>>> root@debian:~# xfs_info /dev/nvme0n1
>>> meta-data=/dev/nvme0n1           isize=512    agcount=8,
>>> agsize=268435455 blks
>>
>> Well max power-of-2 factor of this is going to be 1.
>>
> 
> Exactly. I get that we should restrict max_opt to be 1 because the AG's
> will not be aligned and the best we can do is one fsblock for HW based
> atomics. Why should we restrict the max (SW atomics limit) to 1 fsblock?
> 

Maybe in this case we don't need to restrict CoW-based atomics to 1 
fsblock. But why care? I mean, you have HW support, which is so much 
better to use than CoW-based atomics, so better to config your FS to 
avail of them.