linux-kernel - Re: [PATCH v4 6/9] rbtree: Implement generic latch

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Message-ID: <20150409165917.GQ21418@twins.programming.kicks-ass.net>
Date:	Thu, 9 Apr 2015 18:59:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Ingo Molnar <mingo@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michel Lespinasse <walken@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v4 6/9] rbtree: Implement generic latch_tree

On Thu, Apr 09, 2015 at 09:31:16AM -0700, Linus Torvalds wrote:
> On Thu, Apr 9, 2015 at 5:13 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> >  struct latch_tree_node {
> > +       struct rb_node node[2];
> >  };
> >
> > +static __always_inline struct latch_tree_node *
> > +__lt_from_rb(struct rb_node *node, int idx)
> > +{
> > +       return container_of(node, struct latch_tree_node, node[idx]);
> > +}
> 
> Ugh. That syntax of offset_of() worries me a bit, but some grepping
> shows that we already use this form of offset_of() in parts of the
> kernel, so I guess it's fine.

I was a little surprised myself it worked, but its a constant after
all so it 'should'.

> Even with that small "Ugh", I do have to admit to preferring this to
> having the back-pointer.

Yeah me too, I'll respin the patches proper after I've given it some
actual runtime too.
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