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

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Date:	Thu, 9 Apr 2015 10:12:07 -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 9:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> I was a little surprised myself it worked, but its a constant after
> all so it 'should'.

Well, it should actually work for non-constants too, even when that
'idx' isn't inlined to one of the fixed constants. So even if this
will ever hit the "seq & 1" case for lookup, it should all work. It's
just an expression, after all.

All that is really required is that you can do '&(x->y)' on it, where
'x' is the type, and 'y' is the "member".

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.

                        Linus
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