linux-kernel - Re: [PATCH] dax: Fix last_page check in __bdev_dax

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Message-Id: <87bm01mylr.fsf@vajain21.in.ibm.com>
Date:   Fri, 17 May 2019 11:06:16 +0530
From:   Vaibhav Jain <vaibhav@...ux.ibm.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Chandan Rajendra <chandan@...ux.ibm.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: Re: [PATCH] dax: Fix last_page check in __bdev_dax_supported()

Dan Williams <dan.j.williams@...el.com> writes:

> On Wed, May 15, 2019 at 10:55 PM Vaibhav Jain <vaibhav@...ux.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
>> '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?
>
> https://lore.kernel.org/lkml/155789172402.748145.11853718580748830476.stgit@dwillia2-desk3.amr.corp.intel.com/

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

So, please ignore this patch.

-- 
Vaibhav Jain <vaibhav@...ux.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.