[PATCH 2/2] block: remove the per-bio/request write hint.

[Manjong Lee]

>On Sun, ddMar 06, 2022 at 11:06:12AM -0700, Jens Axboe wrote:
>> On 3/6/22 11:01 AM, Christoph Hellwig wrote:
>> > On Sun, Mar 06, 2022 at 10:11:46AM -0700, Jens Axboe wrote:
>> >> Yes, I think we should kill it. If we retain the inode hint, the f2fs
>> >> doesn't need a any changes. And it should be safe to make the per-file
>> >> fcntl hints return EINVAL, which they would on older kernels anyway.
>> >> Untested, but something like the below.
>> > 
>> > I've sent this off to the testing farm this morning, but EINVAL might
>> > be even better:
>> > 
>> > http://git.infradead.org/users/hch/block.git/shortlog/refs/heads/more-hint-removal
>
>Yup, I like that.
>
>> I do think EINVAL is better, as it just tells the app it's not available
>> like we would've done before. With just doing zeroes, that might break
>> applications that set-and-verify. Of course there's also the risk of
>> that since we retain inode hints (so they work), but fail file hints.
>> That's a lesser risk though, and we only know of the inode hints being
>> used.
>
>Agreed, I think EINVAL would be better here - jsut make it behave
>like it would on a kernel that never supported this functionality in
>the first place. Seems simpler to me for user applications if we do
>that.
>
>Cheers,
>
>Dave.
>-- 
>Dave Chinner
>david at fromorbit.com
>

Currently, UFS device also supports hot/cold data separation 
and uses existing write_hint code.

In other words, the function is also being used in storage other than NVMe,
and if it is removed, it is thought that there will be an operation problem.

If the code is removed, I am worried about how other devices
that use the function.

Is there a good alternative?