linux-kernel - Re: [patch 02/23] SLUB: Rename NUMA defrag_ratio to remote_node_defrag

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Message-ID: <20071108194735.GW19691@waste.org>
Date:	Thu, 8 Nov 2007 13:47:35 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Mel Gorman <mel@...net.ie>, akpm@...ux-foundatin.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 02/23] SLUB: Rename NUMA defrag_ratio to remote_node_defrag_ratio

On Thu, Nov 08, 2007 at 11:16:33AM -0800, Christoph Lameter wrote:
> On Thu, 8 Nov 2007, Matt Mackall wrote:
> 
> > > I cannot figure out what the number of cycles currently showing on the TSC
> > > have to do with a ratio :(. I could semi-understand if we were counting up
> > > how many cycles were being spent trying to pack objects but that does not
> > > appear to be the case. The comment didn't help a whole lot either. It felt
> > > like a cost for packing, not a ratio
> > 
> > It's just a random number generator. And a bad one: lots of arches
> > return 0. And I believe at least one of them has some NUMA support.
> 
> Do we have a better one? Something with minimal processing overhead? I'd 
> be glad to switch it.

Not really. drivers/char/random.c does:

__get_cpu_var(trickle_count)++ & 0xfff

for a similar purpose.

-- 
Mathematics is the supreme nostalgia of our time.
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