On Wed, May 15, 2019 at 10:55 PM Vaibhav Jain <vaibhav(a)linux.ibm.com> wrote:
Presently __bdev_dax_supported() checks if first sector of last
page ( last_page ) on the block device is aligned to page
boundary. However the code to compute 'last_page' assumes that there
are 8 sectors/page assuming a 4K page-size.
This assumption breaks on architectures which use a different page
size specifically PPC64 where page-size == 64K. Hence a warning is
seen while trying to mount a xfs/ext4 file-system with dax enabled:
$ sudo mount -o dax /dev/pmem0 /mnt/pmem
XFS (pmem0): DAX enabled. Warning: EXPERIMENTAL, use at your own risk
XFS (pmem0): DAX unsupported by block device. Turning off DAX.
The patch fixes this issue by updating calculation of 'last_var' to
take into account number-of-sectors/page instead of assuming it to be
Yes, I noticed this too and fixed it up in a wider change that also
allows device-mapper to validate each component device. Does this
patch work for you?