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

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:

quoted

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 
devices.

             		       	       	   - Ted
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