From owner-freebsd-hackers  Wed Jul 25 11: 4:31 2001
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Date: Wed, 25 Jul 2001 14:07:37 -0400
From: Bosko Milekic <bmilekic@technokratis.com>
To: Zhihui Zhang <zzhang@cs.binghamton.edu>
Cc: Terry Lambert <tlambert2@mindspring.com>,
	vishwanath pargaonkar <vishubp@yahoo.com>,
	freebsd-hackers@FreeBSD.ORG
Subject: Re: cluster size
Message-ID: <20010725140737.A25132@technokratis.com>
References: <3B5E69C5.3D3C259E@mindspring.com> <Pine.SOL.4.21.0107251350010.20991-100000@opal>
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In-Reply-To: <Pine.SOL.4.21.0107251350010.20991-100000@opal>; from zzhang@cs.binghamton.edu on Wed, Jul 25, 2001 at 01:51:51PM -0400
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On Wed, Jul 25, 2001 at 01:51:51PM -0400, Zhihui Zhang wrote:
> 
> 
> On Tue, 24 Jul 2001, Terry Lambert wrote:
> 
> > Zhihui Zhang wrote:
> > > > Hi,
> > > > in freebsd can we change the cluster size from 2048
> > > > bytes.If yes how can we do that?
> > > > do we have to configure in some file?
> > > 
> > > You must be asking why the mbuf cluster size is chosen as 2048, right? It
> > > is probably a tradeoff between memory efficient and speed.
> > 
> > Ask yourselves:
> > 
> > 	"What is the minimum cluster size I would have to have
> > 	 to be able to contain the maximum MTU worth of data,
> > 	 yet remain an even multiple of sizeof(mbuf) -- 256
> > 	 bytes?"
> 
> A dumb question: why even not odd multiple?
> 
> -Zhihui

	It actually has to do with the fact that 2K is the only size equal to
or greater than the maximum MTU worth of data that can be multiplied to a page
size without any leftover (in other words, page size modulo 2K is zero).

-- 
 Bosko Milekic
 bmilekic@technokratis.com


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