linux-kernel - Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex

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Message-ID: <20131201125604.GH16796@laptop.programming.kicks-ass.net>
Date:	Sun, 1 Dec 2013 13:56:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Davidlohr Bueso <davidlohr@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Jason Low <jason.low2@...com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mike Galbraith <efault@....de>, Jeff Mahoney <jeffm@...e.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Scott Norton <scott.norton@...com>,
	Tom Vaden <tom.vaden@...com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Waiman Long <Waiman.Long@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket
 plist in futex_wake()

On Sun, Dec 01, 2013 at 01:10:22PM +0100, Ingo Molnar wrote:
> But more importantly, since these are all NUMA systems, would it make 
> sense to create per node hashes on NUMA? Each futex would be enqueued 
> into the hash belonging to its own page's node.

Can't do that; we hash on vaddr, the actual page can move between nodes
while a futex is queued.

This would mean that the waiting futex is queued on another node than
the waker is looking.
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