linux-kernel - Re: [PATCH v3 2/3] fs: Convert kiocb rw

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Date:   Wed, 9 May 2018 15:29:00 +0000
From:   Adam Manzanares <Adam.Manzanares@....com>
To:     Jens Axboe <axboe@...nel.dk>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "bcrl@...ck.org" <bcrl@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: 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:
>> 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
>