Re: [PATCH] dax: Fix last_page check in __bdev_dax_supported()

From: Vaibhav Jain
Date: Fri May 17 2019 - 01:38:34 EST

Dan Williams <dan.j.williams@xxxxxxxxx> writes:

> On Wed, May 15, 2019 at 10:55 PM Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> 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
>> '8'.
> 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?

Thanks Dan, I tested your patch and not seeing the issue anymore.

So, please ignore this patch.

Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>
Linux Technology Center, IBM India Pvt. Ltd.