linux-kernel - Re: [PATCH v2] fs: Add aio iopriority support for block

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Date:   Thu, 3 May 2018 20:58:17 +0000
From:   Adam Manzanares <Adam.Manzanares@....com>
To:     Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>
CC:     "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 v2] fs: Add aio iopriority support for block_dev



On 5/3/18 1:24 PM, Jens Axboe wrote:
> On 5/3/18 2:15 PM, Adam Manzanares wrote:
>>
>>
>> On 5/3/18 11:33 AM, Matthew Wilcox wrote:
>>> On Thu, May 03, 2018 at 11:21:14AM -0700, adam.manzanares@....com wrote:
>>>> If we want to avoid bloating struct kiocb, I suggest we turn the private field
>>>> into a union of the private and ki_ioprio field. It seems like the users of
>>>> the private field all use it at a point where we can yank the priority from
>>>> the kiocb before the private field is used. Comments and suggestions welcome.
>>>
>>> Or we could just make ki_hint a u8 or u16 ... seems unlikely we'll need
>>> 32 bits of ki_hint.  (currently defined values are 1-5)
>>
>> I like the approach of using a u16 for the ki_hint. I'll update and
>> resubmit.
> 
> It's intended to be a mask. If you do shrink it for now, then we need some
> guard code to ensure it can always carry what it needs to.
> 

Got it, I'll add the guard to rw_hint_valid along with a comment about 
being limited by the size of ki_hint in case we get to a situation where 
16 bits is not enough.