linux-kernel - Re: [PATCH v4 1/2] rcu/tree: Add basic support for kfree

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Date:   Sat, 17 Aug 2019 01:53:29 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>,
        kernel-team <kernel-team@....com>,
        Byungchul Park <byungchul.park@....com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Byungchul Park <max.byungchul.park@...il.com>,
        Rao Shoaib <rao.shoaib@...cle.com>, rcu <rcu@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v4 1/2] rcu/tree: Add basic support for kfree_rcu()
 batching

On Fri, Aug 16, 2019 at 10:20:23PM -0700, Paul E. McKenney wrote:
> On Sat, Aug 17, 2019 at 12:30:24AM -0400, Joel Fernandes wrote:
> > On Fri, Aug 16, 2019 at 08:56:37PM -0700, Paul E. McKenney wrote:
> > > On Fri, Aug 16, 2019 at 09:32:23PM -0400, Joel Fernandes wrote:
> > > > Hi Paul,
> > > > 
> > > > On Fri, Aug 16, 2019 at 3:16 PM Paul E. McKenney <paulmck@...ux.ibm.com> wrote:
> > > > > > > Hello, Joel,
> > > > > > >
> > > > > > > I reworked the commit log as follows, but was then unsuccessful in
> > > > > > > working out which -rcu commit to apply it to.  Could you please
> > > > > > > tell me what commit to apply this to?  (Once applied, git cherry-pick
> > > > > > > is usually pretty good about handling minor conflicts.)
> > > > > >
> > > > > > It was originally based on v5.3-rc2
> > > > > >
> > > > > > I was able to apply it just now to the rcu -dev branch and I pushed it here:
> > > > > > https://github.com/joelagnel/linux-kernel.git (branch paul-dev)
> > > > > >
> > > > > > Let me know if any other issues, thanks for the change log rework!
> > > > >
> > > > > Pulled and cherry-picked, thank you!
> > > > >
> > > > > Just for grins, I also  pushed out a from-joel.2019.08.16a showing the
> > > > > results of the pull.  If you pull that branch, then run something like
> > > > > "gitk v5.3-rc2..", and then do the same with branch "dev", comparing the
> > > > > two might illustrate some of the reasons for the current restrictions
> > > > > on pull requests and trees subject to rebase.
> > > > 
> > > > Right, I did the compare and see what you mean. I guess sending any
> > > > future pull requests against Linux -next would be the best option?
> > > 
> > > Hmmm...  You really want to send some pull requests, don't you?  ;-)
> > 
> > I would be lying if I said I don't have the itch to ;-)
> > 
> > > Suppose you had sent that pull request against Linux -next or v5.2
> > > or wherever.  What would happen next, given the high probability of a
> > > conflict with someone else's patch?  What would the result look like?
> > 
> > One hopes that the tools are able to automatically resolve the resolution,
> > however adequate re-inspection of the resulting code and testing it would be
> > needed in either case, to ensure the conflict resolution (whether manual or
> > automatic) happened correctly.
> 
> I didn't ask you to hope.  I instead asked you what tell me what would
> actually happen.  ;-)
> 
> You could actually try this by randomly grouping the patches in -rcu
> (say, placing every third patch into one of three groups), generating
> separate pull requests, and then merging the pull requests together.
> Then you wouldn't have to hope.  You could instead look at it in (say)
> gitk after the pieces were put together.

So you take whatever is worked on in 'dev' and create separate branches out
of them, then merge them together later?

I have seen you doing these tricks and would love to get ideas from your
experiences on these.

> > IIUC, this usually depends on the maintainer's preference on which branch to
> > send patches against.
> > 
> > Are you saying -rcu's dev branch is still the best option to send patches
> > against, even though it is rebased often?
> 
> Sounds like we might need to discuss this face to face.

Yes, let us talk for sure at plumbers, thank you so much!

(Also I sent a patch just now to fix that xchg() issue).

 - Joel