Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io

[Dan Williams]

On Fri, Apr 15, 2016 at 11:06 AM, Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> Dan Williams <dan.j.williams@xxxxxxxxx> writes:
>
>>>> There's a lot of special casing here, so you might consider adding
>>>> comments.
>>>
>>> Correct - maybe we should reconsider wrapper-izing this? :)
>>
>> Another option is just to skip dax_do_io() and this special casing
>> fallback entirely if errors are present.  I.e. only attempt dax_do_io
>> when: IS_DAX() && gendisk->bb && bb->count == 0.
>
> So, if there's an error anywhere on the device, penalize all I/O (not
> just writes, and not just on sectors that are bad)?  I'm not sure that's
> a great plan, either.
>

If errors are rare how much are we actually losing in practice?
Moreover, we're going to do the full badblocks lookup anyway when we
call ->direct_access().  If we had that information earlier we can
avoid this fallback dance.