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Re: regression introduced by "block: Add support for DAX reads/writes to block devices"

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On 8/13/2015 10:00 AM, Jeff Moyer wrote:
> Boaz Harrosh <boaz@plexistor.com> writes:
> 
>> On 08/13/2015 12:11 AM, Jeff Moyer wrote:
>>> Boaz Harrosh <boaz@plexistor.com> writes:
>>>
>>>> On 08/07/2015 11:41 PM, Jeff Moyer wrote:
>>>> <>
>>>>>
>>>>>> We need to cope with the case where the end of a partition isn't on a
>>>>>> page boundary though.
>>>>>
>>>>> Well, that's usually done by falling back to buffered I/O.  I gave that
>>>>> a try and panicked the box.  :)  I'll keep looking into it, but probably
>>>>> won't have another patch until next week.
>>>>>
>>>>
>>>> lets slow down for a sec, please.
>>>>
>>>> We have all established that an unaligned partition start is BAD and not supported?
>>>
>>> No.  Unaligned partitions on RAID arrays or 512e devices are bad because
>>> they result in suboptimal performance.  They are most certainly still
>>> supported, though.
>>>
>>
>> What ?
>>
>> I meant for dax on pmem or brd. I meant that we *do not* support dax access
>> on an unaligned partition start. (None dax is perfectly supported)
> 
> Sorry, I thought your statement was broader than that.
> 
>> We did it this way because of the direct_access API that returns a pfn
>> with is PAGE_SIZE. We could introduce a pfn+offset but we thought it is
>> not worth it, and that dax should be page aligned for code simplicity
> 
> I'd be fine with changing the persistent memory block device to only
> support 4k logical, 4k physical block size.  That probably makes the
> most sense.

If that's what we want, the current patch doesn't do that.
https://lists.01.org/pipermail/linux-nvdimm/2015-July/001555.html

It causes the physical block size to be PAGE_SIZE but the
logical block size is still 512.  However, the minimum_io_size
is now 4096 (same as physical block size, I assume).  The
optimal_io_size is still 0.  What does that mean?

Whatever we go with, we should do something because 4.2rc6 is still
broken, unable to create a xfs file system on a pmem device, ever
since the change to use DAX on block devices with O_DIRECT.

-- ljk
> 
> Cheers,
> Jeff
> 

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regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-05 22:20 +0200
  Re: regression introduced by "block: Add support for DAX  reads/writes to block devices" Dave Chinner <david@fromorbit.com> - 2015-08-06 00:10 +0200
    Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Linda Knippers <linda.knippers@hp.com> - 2015-08-06 03:50 +0200
      Re: regression introduced by "block: Add support for DAX  reads/writes to block devices" Dave Chinner <david@fromorbit.com> - 2015-08-06 05:30 +0200
        Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Boaz Harrosh <boaz@plexistor.com> - 2015-08-06 10:00 +0200
          Re: regression introduced by "block: Add support for DAX  reads/writes to block devices" Dave Chinner <david@fromorbit.com> - 2015-08-06 22:40 +0200
            Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Boaz Harrosh <boaz@plexistor.com> - 2015-08-09 11:00 +0200
              Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Linda Knippers <linda.knippers@hp.com> - 2015-08-10 18:40 +0200
                Re: regression introduced by "block: Add support for DAX  reads/writes to block devices" Dave Chinner <david@fromorbit.com> - 2015-08-10 23:30 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Linda Knippers <linda.knippers@hp.com> - 2015-08-11 01:10 +0200
  RE: regression introduced by "block: Add support for DAX  reads/writes to block devices" "Wilcox, Matthew R" <matthew.r.wilcox@intel.com> - 2015-08-06 16:30 +0200
    Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-06 17:40 +0200
      RE: regression introduced by "block: Add support for DAX  reads/writes to block devices" "Wilcox, Matthew R" <matthew.r.wilcox@intel.com> - 2015-08-06 18:00 +0200
    Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-07 00:30 +0200
      RE: regression introduced by "block: Add support for DAX  reads/writes to block devices" "Wilcox, Matthew R" <matthew.r.wilcox@intel.com> - 2015-08-07 20:20 +0200
        Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-07 22:50 +0200
          Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Boaz Harrosh <boaz@plexistor.com> - 2015-08-10 09:50 +0200
            Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-12 23:20 +0200
              Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Boaz Harrosh <boaz@plexistor.com> - 2015-08-13 07:40 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-13 16:10 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Linda Knippers <linda.knippers@hp.com> - 2015-08-13 18:50 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-13 19:20 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Linda Knippers <linda.knippers@hp.com> - 2015-08-13 20:00 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Jeff Moyer <jmoyer@redhat.com> - 2015-08-13 20:20 +0200
                RE: regression introduced by "block: Add support for DAX  reads/writes to block devices" "Wilcox, Matthew R" <matthew.r.wilcox@intel.com> - 2015-08-13 21:40 +0200
                Re: regression introduced by "block: Add support for DAX reads/writes  to block devices" Dan Williams <dan.j.williams@intel.com> - 2015-08-14 18:30 +0200

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