linux-kernel - Re: [PATCH 0/2] Remove kiocb ki

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Message-ID: <20200709133249.GC12769@casper.infradead.org>
Date:   Thu, 9 Jul 2020 14:32:49 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kanchan Joshi <joshi.k@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>
Subject: Re: [PATCH 0/2] Remove kiocb ki_complete

On Thu, Jul 09, 2020 at 02:26:11PM +0100, Christoph Hellwig wrote:
> On Thu, Jul 09, 2020 at 12:10:36PM +0100, Matthew Wilcox wrote:
> > On Thu, Jul 09, 2020 at 11:17:05AM +0100, Christoph Hellwig wrote:
> > > I really don't like this series at all.  If saves a single pointer
> > > but introduces a complicated machinery that just doesn't follow any
> > > natural flow.  And there doesn't seem to be any good reason for it to
> > > start with.
> > 
> > Jens doesn't want the kiocb to grow beyond a single cacheline, and we
> > want the ability to set the loff_t in userspace for an appending write,
> > so the plan was to replace the ki_complete member in kiocb with an
> > loff_t __user *ki_posp.
> > 
> > I don't think it's worth worrying about growing kiocb, personally,
> > but this seemed like the easiest way to make room for a new pointer.
> 
> The user offset pointer has absolutely no business in the the kiocb
> itself - it is a io_uring concept which needs to go into the io_kiocb,
> which has 14 bytes left in the last cache line in my build.  It would
> fit in very well there right next to the result and user pointer.

I agree.  Jens doesn't.