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

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Message-ID: <20210127183152.GP740243@zeniv-ca>
Date:   Wed, 27 Jan 2021 18:31:52 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Pavel Begunkov <asml.silence@...il.com>
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 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...