linux-kernel - Re: [patch][rfc] ddds: "dynamic dynamic data structure" algorithm, for adaptive dcache hash table sizing

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Message-ID: <20081008031245.GC7101@linux.vnet.ibm.com>
Date:	Tue, 7 Oct 2008 20:12:45 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-netdev@...r.kernel.org,
	josh@...edesktop.org
Subject: Re: [patch][rfc] ddds: "dynamic dynamic data structure" algorithm,
	for adaptive dcache hash table sizing

On Wed, Oct 08, 2008 at 04:48:13AM +0200, Nick Piggin wrote:
> On Tue, Oct 07, 2008 at 02:08:25PM -0700, David Miller wrote:
> > From: Nick Piggin <npiggin@...e.de>
> > Date: Tue, 7 Oct 2008 08:48:34 +0200
> > 
> > > I'm cc'ing netdev because Dave did express some interest in using this for
> > > some networking hashes, and network guys in general are pretty cluey when it
> > > comes to hashes and such ;)
> > 
> > Interesting stuff.
> > 
> > Paul, many months ago, forwarded to me a some work done by Josh
> > Triplett called "rcuhashbash" which had similar objectives.  He did
> > post it to linux-kernel, and perhaps even your ideas are inspired by
> > his work, I don't know. :-)
> 
> Hmm yes I did see that. It's not too similar, as it focuses on re-keying
> an existing element into the same hash table. ddds can't do that kind of
> thing (the underlying data structure isn't visible to the algorithm, so
> it can't exactly modify data structures in-place), although in another
> sense it is more general because the transfer function could transfer
> items into another hash table and re-key them as it goes (if it did that,
> it could probably use Josh's "atomic" re-keying algorithm too).
> 
> But largely it does seem like they are orthogonal (if I'm reading
> rcuhashbash correctly).

IIRC, one of the weaknesses of rcuhashbash was that the elements had
to be copied in some cases.  Josh has been working on a variant that
(hopefully) allows elements to be moved without copying, as is required
by dcache.

							Thanx, Paul
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