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From: Dave Chinner <>
To: Allison Collins <>
Cc: Amir Goldstein <>,
	"Darrick J. Wong" <>,,
	linux-fsdevel <>,
	xfs <>, Eryu Guan <>,
	Eric Sandeen <>
Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] FS Maintainers Don't Scale
Date: Thu, 13 Feb 2020 10:39:29 +1100
Message-ID: <20200212233929.GS10776@dread.disaster.area> (raw)
In-Reply-To: <>

Hi Allison,

These are some very good observations and questions. I've found it
hard to write a meaningful response because there are many things I
just take for granted having done this for many many years...

I don't have all the answers. Lots of what I say is opinion (see my
comments about opinions below!) based on experience and the best I
can do to help improve the situation is to share what I think and
let people reading this decide what might be useful to their own

On Sun, Feb 09, 2020 at 10:12:03AM -0700, Allison Collins wrote:
> On 2/2/20 2:46 PM, Dave Chinner wrote:
> > On Fri, Jan 31, 2020 at 08:20:37PM -0700, Allison Collins wrote:
> > > On 1/31/20 12:30 AM, Amir Goldstein wrote:
> > > > On Fri, Jan 31, 2020 at 7:25 AM Darrick J. Wong <> wrote:
> > > > Bottom line - a report of the subsystem review queue status, call for
> > > > reviewers and highlighting specific areas in need of review is a good idea.
> > > > Developers responding to that report publicly with availability for review,
> > > > intention and expected time frame for taking on a review would be helpful
> > > > for both maintainers and potential reviewers.
> > > I definitely think that would help delegate review efforts a little more.
> > > That way it's clear what people are working on, and what still needs
> > > attention.
> > 
> > It is not the maintainer's repsonsibility to gather reviewers. That
> > is entirely the responsibility of the patch submitter. That is, if
> > the code has gone unreviewed, it is up to the submitter to find
> > people to review the code, not the maintainer. If you, as a
> > developer, are unable to find people willing to review your code
> > then it's a sign you haven't been reviewing enough code yourself.
> > 
> > Good reviewers are a valuable resource - as a developer I rely on
> > reviewers to get my code merged, so if I don't review code and
> > everyone else behaves the same way, how can I possibly get my code
> > merged? IOWs, review is something every developer should be spending
> > a significant chunk of their time on. IMO, if you are not spending
> > *at least* a whole day a week reviewing code, you're not actually
> > doing enough code review to allow other developers to be as
> > productive as you are.
> > 
> > The more you review other people's code, the more you learn about
> > the code and the more likely other people will be to review your
> > code because they know you'll review their code in turn.  It's a
> > positive reinforcement cycle that benefits both the individual
> > developers personally and the wider community.
> > 
> > But this positive reinforcemnt cycle just doesn't happen if people
> > avoid reviewing code because they think "I don't know anything so my
> > review is not going to be worth anything".  Constructive review, not
> > matter whether it's performed at a simple or complex level, is
> > always valuable.
> > 
> > Cheers,
> > 
> > Dave.
> > 
> Well, I can see the response is meant to be encouraging, and you are right
> that everyone needs to give to receive :-)
> I have thought a lot about this, and I do have some opinions about it how
> the process is described to work vs how it ends up working though. There has
> quite been a few times I get conflicting reviews from multiple reviewers. I
> suspect either because reviewers are not seeing each others reviews, or
> because it is difficult for people to recall or even find discussions on
> prior revisions.  And so at times, I find myself puzzling a bit trying to
> extrapolate what the community as a whole really wants.

IMO, "what the community wants" really doesn't matter in the end;
the community really doesn't know what it wants.  Note: I'm not
saying that "the community doesn't matter", what I'm trying to say
is that the community is full of diverse opinions and that they are
just that: opinions. And in the end, it's the code that is preserved
forever and the opinions get forgotten.

It's also worth reminding yourself that the author of the code is
also part of the community, and that they are the only community
member that has direct control of the changes that will be made to
the code.  Hence, to me, the only thing that really matters is
answering this question: "What am I, the author of this code,
willing to compromise on to get this code merged?"

That comes down to separating fact from opinion - review comments
are often opinion. e.g. A reviewer finds a bug then suggests how to
fix it.  There are two things here - the bug is fact, the suggested
fix is opinion. The fact needs to be addressed (i.e. the bug must be
fixed), but it does not need to be fixed the way the reviewer
suggested as that is an opinion.

Hence it can be perfectly reasonable to both agree with and disagree
with the reviewer on the same topic. Separate the fact from the
opinion, address the facts and then decide if the opinion improves
the code you have or not.  You may end up may using some, all or
none of the reviewer's suggestion, but just because it was suggested
it doesn't mean you have to change the code that way. The code
author is ultimately in control of the process here.

IMO, people need to be better at saying "no" and accepting "no" as a
valid answer (both code authors and reviewers). "No" is not a
personal rejection, it's just a simple, clear statement that
further progress will not be made by continuing down that path and a
different solution/compromise will have to be found.

> For example: a reviewer may propose a minor change, perhaps a style change,
> and as long as it's not terrible I assume this is just how people are used
> to seeing things implemented.  So I amend it, and in the next revision
> someone expresses that they dislike it and makes a different proposition.

At which point you need to say "no". :) Probably with the
justification that this is "rearranging the deck chairs/painting the
bikeshed again".

I do understand that it might be difficult to ignore suggestions
that people like Darrick, myself, Christoph, etc might make.
However, you should really ignore who the suggestion came from while
thinking about whether it is actually a valuable or necessary
change. ie. don't make a change just because of the _reputation_ of
the person who suggested it.

> Generally I'll mention that this change was requested, but if
> anyone feels particularly strongly about it, to please chime in.
> Most of the time I don't hear anything, I suspect because either
> the first reviewer isn't around, or they don't have time to
> revisit it?  Maybe they weren't strongly opinionated about it to
> begin with?  It could have been they were feeling pressure to
> generate reviews, or maybe an employer is measuring their
> engagement?  In any case, if it goes around a third time, I'll
> usually start including links to prior reviews to try and get
> people on the same page, but most of the time I've found the
> result is that it just falls silent.
> At this point though it feels unclear to me if everyone is happy?

IMO, "everyone is happy" is not acheivable. Trying to make everyone
happy simply leads to stalemate situations where the necessary
compromises to make progress cannot be made because they'll always
make someone "unhappy".

Hence for a significant patchset I always strive for "everyone is
a bit unhappy" as the end result. If everyone is unhappy, it means
everyone has had to compromise in some way to get the work merged.
And I most certainly include myself in the "everyone is unhappy"
group, too.

To reinforce that point, I often issue rvb tags for code that is
functionally correct and does what is needed, but I'm not totally
happy with for some reason (e.g. structure, not the way I'd solve
the problem, etc).  Preventing that code from being merged because
it's not written exactly the way I'd write/solve it is petty and
nobody wins when that happens. Yes, I'd be happier if it was
different, but it's unreasonable to expect the author to do things
exactly the way I'd like it to be done.

This sort of "unhappy but OK" compromise across the board is
generally the best you can hope for. And it's much easier to deal
with competing reviews if you aim for such an "everyone unhappy"
compromise rather than searching for the magic "everyone happy"

> Did we have a constructive review?  Maybe it's not a very big deal
> and I should just move on.  And in many scenarios like the one
> above, the exact outcome appears to be of little concern to people
> in the greater scheme of things.

Exactly - making everyone happy about the code doesn't really
matter. What matters is finding the necessary compromise that will
get the code merged. Indeed, it's a bit of a conundrum - getting the
code merged is what makes people happy, but before that happens you
have to work to share the unhappiness around. :/

> But this pattern does not always
> scale well in all cases.  Complex issues that persist over time
> generally do so because no one yet has a clear idea of what a
> correct solution even looks like, or perhaps cannot agree on one.
> In my experience, getting people to come together on a common goal
> requires a sort of exploratory coding effort. Like a prototype
> that people can look at, learn from, share ideas, and then adapt
> the model from there.

Right, that's pretty common. Often I'll go through 3 or 4 private
prototypes before I even get to posting something on the mailing
list, and then it will take another couple of iterations because
other people start to understand the code. And then another couple
of iterations for them to become comfortable with the code and start
to have really meaningful suggestions for improvement.

> But for that to work, they need to have
> been engaged with the history of it.  They need the common
> experience of seeing what has worked and what hasn't.  It helps
> people to let go of theories that have not performed well in
> practice, and shift to alternate approaches that have.  In a way,
> reviewers that have been historically more involved with a
> particular effort start to become a little integral to it as its
> reviewers.

"reviewers turn into collaborators".

That, in itself, is not a bad thing.

However if you get no other reviewers you'll never get a fresh
persepective, and if your reviewers don't have the necessary
expertise the collaboration won't result in better code. It also
tends to sideline people who think the problem should be tackled a
different way. We don't want review to be a rubber stamp issued by
"yes people". We want people who disagree to voice their
disagreement and ask for change because that's how we improve the

Personally, I do not review every version of every patchset simply
because I don't have the time to do that.  Hence I tend to do design
review on early patchset iterations rather than code reviews.
I need to understand the design and structure of the
change before I'll be able to look at the detail of the code and
understand whether it is correct or not. Hence I might do an early
design review from reading the patches and make high level comments,
then skip the next 3-4 iterations where the code changes
significantly as bugs are fixed and code is cleaned up. Then I'll go
back and look at the code in detail and perform an actual code
review, and I will not have any idea about what was said in the
previous review iterations. And I'll come back every 3-4 versions of
the patchset, too.

IMO, expecting reviewers to know everything that happened in all the
previous reviews is unrealistic.  If there is some reason for the
code being the way it is and it is not documented in the patch, then
the change needs more work. "Why is the code like this?" followed
by "please document this in a comment" is a reasonable review
request and you won't get those questions from reviewers who look at
every version of the patchset because they are familiary with the
history of the code.

If this sort of question is not asked during review, we end up in
the situation where someone looks at the code a year after it is
merged and there's no documentation in the code or commit messages
that explains why the code is written the way it is. This is what
makes drive-by reviews valuable - people unfamiliar with the code
see it differently and ask different questions....

IOWs, everyone is free to review code at any time with no
constraints, past requirements or future liabilities.  If the code
author wants someone to review every version of a patchset, then
they need to co-ordinate those people to set aside the time to
review the code in a prompt and efficient manner. However, expecting
that other developers cannot review a V5 patchset without first
having read all of the reviews of v1-v4 is unrealistic, especially
as this reduces the value of their review substantially as their
viewpoint is now "tainted" by knowing the history of the code up to
this point....

> Which I *think* is what Darrick may be eluding to in
> his initial proposition.  People request for certain reviewers, or
> perhaps the reviewers can volunteer to be sort of assigned to it
> in an effort to provide more constructive reviews.  In this way,
> reviewers allocate their efforts where they are most effective,
> and in doing so better distribute the work load as well.  Did I
> get that about right?  Thoughts?

[ speaking as someone who was almost completely burnt out by
having to perform most of the review, testing and maintanence tasks
for kernel, userspace and test infrastructue for several years ]

Again, I don't think the maintainer should have anything to do with
this process. Distributed development requires peers to collaborate
and self organise without central coordination of their efforts.
Hence it is the responsibility of the code author to organise review
for code they are working on. The code author wants the code merged,
therefore they are the people with the motivation to get the code
reviewed promptly.

And, quite frankly, the maintainer has no power to force someone to
review code. Hence asking the maintainer to manage reviewers on
behalf of code authors won't work any better than
distributing/delegating that responsibility to the code author...

Historically speaking, the XFS maintainer's prime reponsibility has
been to merge community reviewed code into the upstream tree, not to
review code or tell people what code they should be reviewing. The
fact that we are still placing the burden of review and
co-ordinating review on the maintainer despite ample evidence that
it causes burn-out is a failure of our community to self-organise
and protect our valuable resources....


Dave Chinner

  parent reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31  5:25 Darrick J. Wong
2020-01-31  7:30 ` [Lsf-pc] " Amir Goldstein
2020-02-01  3:20   ` Allison Collins
2020-02-02 21:46     ` Dave Chinner
2020-02-09 17:12       ` Allison Collins
2020-02-12  0:21         ` NeilBrown
2020-02-12  6:58           ` Darrick J. Wong
2020-02-12 22:06         ` Darrick J. Wong
2020-02-12 22:19           ` Dan Williams
2020-02-12 22:36             ` Darrick J. Wong
2020-02-13 15:11           ` Brian Foster
2020-02-13 15:46             ` Matthew Wilcox
2020-02-16 21:55               ` Dave Chinner
2020-02-19  0:29                 ` Darrick J. Wong
2020-02-19  1:17                   ` Theodore Y. Ts'o
2020-02-12 23:39         ` Dave Chinner [this message]
2020-02-13 15:19           ` Brian Foster
2020-02-17  0:11             ` Dave Chinner
2020-02-17 15:01               ` Brian Foster
2020-02-12 21:36       ` Darrick J. Wong
2020-02-12 22:42   ` Darrick J. Wong
2020-02-13 10:21     ` Amir Goldstein
2020-02-07 22:03 ` Matthew Wilcox
2020-02-12  3:51   ` Theodore Y. Ts'o
2020-02-12 22:29     ` Darrick J. Wong
2020-02-12 22:21   ` Darrick J. Wong
2020-02-13  1:23     ` Dave Chinner

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