linux-kernel - Re: [rfc][patch] dynamic resizing dentry hash using RCU

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Date:	Fri, 23 Feb 2007 17:31:30 -0800
From:	"Michael K. Edwards" <medwards.linux@...il.com>
To:	"Zach Brown" <zab@...bo.net>
Cc:	"Nick Piggin" <npiggin@...e.de>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Davide Libenzi" <davidel@...ilserver.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [rfc][patch] dynamic resizing dentry hash using RCU

On 2/23/07, Zach Brown <zab@...bo.net> wrote:
> I'd love to see a generic implementation of RCU hashing that
> subsystems can then take advantage of.  It's long been on the fun
> side of my todo list.  The side I never get to :/.

There's an active thread on netdev about implementing an RCU hash.
I'd suggest a 2-left (or possibly even k-left) hash for statistical
reasons discussed briefly there, and in greater depth in a paper by
Michael Mitzenmacher at
www.eecs.harvard.edu/~michaelm/NEWWORK/postscripts/iproute.ps.
Despite his paper's emphasis on hardware parallelism, there's a bigger
win associated with Poisson statistics and decreasing occupation
fraction (and therefore collision probability) in successive hashes.

Cheers,
- Michael
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