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

From: Boaz Harrosh
Date: Thu Aug 13 2015 - 01:32:33 EST

On 08/13/2015 12:11 AM, Jeff Moyer wrote:
> Boaz Harrosh <boaz@xxxxxxxxxxxxx> 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)

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


> -Jeff

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