Re: [PATCH v3 2/3] fs: Convert kiocb rw_hint from enum to u16

From: Adam Manzanares
Date: Wed May 09 2018 - 11:29:14 EST

On 5/9/18 11:21 AM, Theodore Y. Ts'o wrote:
> On Wed, May 09, 2018 at 08:23:00AM -0600, Jens Axboe wrote:
>> Streams is essentially the only thing ki_hint is currently used for,
>> with the write life time hints mapping to a stream. The idea for the
>> user side API was to have other things than just write life time hints.
>> Since Adam wants to do priorities, he'd either need to pack into the
>> existing ki_hint, or do this patch does, which is make it smaller and
>> add a new member. I think the latter is cleaner.
> Fair enough; but maybe we can use a u8 instead of a u16? 65,535
> priorities still seem like way more than would ever make sense. I
> think 256 priorities is still way to many, but it's simpler while
> still reserving number of bits for future se.

The intention was to mimic the ioprio_set system call, which uses 3 bits
for a prio class and 13 bits for a prio_value.

IDK what is the right amount of bits to use, but the existing use of
bits seemed flexible enough to support many types of applications and
> - Ted