Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

[Yang, Xiao/杨 晓]

On 2022/9/14 14:44, Yang, Xiao/杨 晓 wrote:
> On 2022/9/9 21:01, Brian Foster wrote:
> > Yes.. I don't recall all the internals of the tools and test, but IIRC
> > it relied on discard to perform zeroing between checkpoints or some such
> > and avoid spurious failures. The purpose of running on dm-thin was
> > merely to provide reliable discard zeroing behavior on the target device
> > and thus to allow the test to run reliably.
> Hi Brian,
>
> As far as I know, generic/470 was original designed to verify
> mmap(MAP_SYNC) on the dm-log-writes device enabling DAX. Due to the
> reason, we need to ensure that all underlying devices under
> dm-log-writes device support DAX. However dm-thin device never supports
> DAX so
> running generic/470 with dm-thin device always returns "not run".
>
> Please see the difference between old and new logic:
>
>            old logic                          new logic
> ---------------------------------------------------------------
> log-writes device(DAX)                 log-writes device(DAX)
>              |                                       |
> PMEM0(DAX) + PMEM1(DAX)       Thin device(non-DAX) + PMEM1(DAX)
>                                            |
>                                          PMEM0(DAX)
> ---------------------------------------------------------------
>
> We think dm-thin device is not a good solution for generic/470, is there
> any other solution to support both discard zero and DAX?

Hi Brian,

I have sent a patch[1] to revert your fix because I think it's not good 
for generic/470 to use thin volume as my revert patch[1] describes:
[1] 
https://lore.kernel.org/fstests/20220914090625.32207-1-yangx.jy@xxxxxxxxxxx/T/#u

With the revert, generic/470 can always run successfully on my 
environment so I wonder how to reproduce the out-of-order replay issue 
on XFS v5 filesystem?

PS: I want to reproduce the issue and try to find a better solution to 
fix it.

Best Regards,
Xiao Yang

> BTW, only log-writes, stripe and linear support DAX for now.