linux-kernel - Re: [PATCH] iov_iter: optimise iter type checking

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Message-ID: <baa41253-bf9b-5bac-d044-5264dd8808f7@gmail.com>
Date:   Thu, 28 Jan 2021 11:39:15 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     David Laight <David.Laight@...lab.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iov_iter: optimise iter type checking

On 27/01/2021 18:31, Al Viro wrote:
> On Wed, Jan 27, 2021 at 03:48:10PM +0000, Pavel Begunkov wrote:
>> On 16/01/2021 05:18, Al Viro wrote:
>>> On Sat, Jan 09, 2021 at 10:11:09PM +0000, Pavel Begunkov wrote:
>>>
>>>>> Does any code actually look at the fields as a pair?
>>>>> Would it even be better to use separate bytes?
>>>>> Even growing the on-stack structure by a word won't really matter.
>>>>
>>>> u8 type, rw;
>>>>
>>>> That won't bloat the struct. I like the idea. If used together compilers
>>>> can treat it as u16.
>>>
>>> Reasonable, and from what I remember from looking through the users,
>>> no readers will bother with looking at both at the same time.
>>
>> Al, are you going turn it into a patch, or prefer me to take over?
> 
> I'll massage that a bit and put into #work.iov_iter - just need to dig my
> way from under the pile of ->d_revalidate() review...

Perfect, thanks

-- 
Pavel Begunkov