Message-ID: <CAL+tcoBKZ4FMk9ozFidWUgfrEyRBrHCsh4cMMbTOA_e-wn0UJQ@mail.gmail.com>
Date: Mon, 12 May 2025 10:22:45 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: "Dr. David Alan Gilbert" <linux@...blig.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, andriy.shevchenko@...ux.intel.com, 
	corbet@....net, linux-doc@...r.kernel.org, 
	LKML <linux-kernel@...r.kernel.org>, viro@...iv.linux.org.uk, 
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH] relay: Remove unused relay_late_setup_files

On Mon, May 12, 2025 at 9:30 AM Dr. David Alan Gilbert
<linux@...blig.org> wrote:
>
> * Jason Xing (kerneljasonxing@...il.com) wrote:
> > Hi All,
>
> Hi Jason,
>
> > I noticed this patch "relay: Remove unused relay_late_setup_files"
> > appears in the mm branch already[1], which I totally missed. Sorry for
> > joining the party late.
> >
> > I have a different opinion on this. For me, I'm very cautious about
> > what those so-called legacy interfaces are and how they can work in
> > different cases and what the use case might be... There are still a
> > small number of out-of-tree users like me heavily relying on relayfs
> > mechanism. So my humble opinion is that if you want to remove
> > so-called dead code, probably clearly state why it cannot be used
> > anymore in the future.
>
> We've got lots of deadcode, why it's dead varies a lot; for example
> people forgetting to clean it up after other patches etc - so this
> _could_ be used but hasn't been for well over 7 years.
>
> > Dr. David, I appreciate your patch, but please do not simply do the
> > random cleanup work __here__. If you take a deep look at the relayfs,
> > you may find there are other interfaces/functions no one uses in the
> > kernel tree.
>
> Actually, that was the only interface in relay that I found unused.

Not really. More than this single one, say, __relay_write() and
subbuf_start_reserve()...

>
> > I'm now checking this kind of patch in relayfs one by one to avoid
> > such a thing happening. I'm trying to maintain it as much as possible
> > since we internally use it in the networking area to output useful
> > information in the hot paths, a little bit like blktrace. BTW, relayfs
> > is really a wonderful one that helps kernel modules communicate with
> > userspace very efficiently. I'm trying to revive it if I can.
>
> If you've got a use for that function, then I'm more than happy to suggest
> just dropping my patch.
>
> However, it is a fairly chunky function that is built into distro
> kernels - so I think it should have a little thought put to it.
>
> As I say, if you are using it, it's fine by me just to drop this patch.

For now, I'm not using it but still considering what the use case
might be in the future. As I mentioned earlier, I'm trying to make
relayfs more robust with more realistic functions.

IMHO, it's not really a dead code to me unless you can clarify why
it's obsolete instead of claiming "no one is using it". If you insist
on the point, then most of relayfs would be removed, which is
apparently not what I'm wishing for.

Probably it will be finally removed, but not at the moment. Evidence
is still not clear to me :S

For sure, the last call would be made by Andrew and Jens. Please help
review this patch one more time. Thanks!

Thanks,
Jason

>
> Dave
>
> > [1]: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything&id=46aa76118ee365c25911806e34d28fc2aa5ef997
> >
> > Thanks,
> > Jason
> --
>  -----Open up your eyes, open up your mind, open up your code -------
> / Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \
> \        dave @ treblig.org |                               | In Hex /
>  \ _________________________|_____ http://www.treblig.org   |_______/

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