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

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Message-ID: <CA+55aFwGA4Znv38=TpAA4hrNSjJez-w0_pu88c1Y__+P2THXZA@mail.gmail.com>
Date:	Thu, 9 Apr 2015 10:17:07 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.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 9, 2015 at 10:12 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> It's just unusual, which I think makes it slightly harder to read for
> a *human* just because it breaks the normal pattern of those things.
> But there's nothing technically wrong with it.

You could have written it as

  static __always_inline struct latch_tree_node *
  __lt_from_rb(struct rb_node *node, int idx)
  {
         return (void *)(node-idx);
  }

which is actually shorter, but even if that container_of() use looks a
bit unusual, I think the container_of() shows more clearly what you
actually want. Plus it would be more reliable if you ever end up
adding any other fields to the struct latch_tree_node.

So I wouldn't actually suggest using that "(node-idx)" format. I think
it should result in the exact same code, though.

                         Linus
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