Re: [PATCH v4 5/7] fs: prioritize and separate direct_io from dax_io

From: Boaz Harrosh
Date: Mon May 02 2016 - 15:22:25 EST

On 05/02/2016 09:48 PM, Dan Williams wrote:
>> And then it keeps broken the aligned buffered writes, which are still
>> broken after this set.
> ...identical to the current situation with a traditional disk.

Not true!! please see what I wrote "aligned buffered writes"
If there are no reads involved then there are no errors returned
to application.

>> I have by now read the v2 patches. And I think you guys did not yet try
>> the proper fix for dax_do_io. I think you need to go deeper into the loops
>> and selectively call bdev_* when error on a specific page copy. No need to
>> go through direct_IO path at all.
> We still reach a point where the minimum granularity of
> bdev_direct_access() is larger than a sector, so you end up still
> needing to have the application understand how to send a properly
> aligned I/O. The semantics of how to send a properly aligned
> direct-I/O are already well understood, so we simply reuse that path.

You are making a mountain out of a mouse. The simple copy of a file
from start (offset ZERO) to end-of-file which is the most common usage
on earth is perfectly aligned and needs not any O_DIRECT and is what is used

>> Do you need that I send you a patch to demonstrate what I mean?
> I remain skeptical of what you are proposing, but yes, a patch has a
> better chance to move the discussion forward.

Sigh! OK