From owner-freebsd-hackers Thu Jul 26 10:14:58 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from falcon.mail.pas.earthlink.net (falcon.mail.pas.earthlink.net [207.217.120.74]) by hub.freebsd.org (Postfix) with ESMTP id CE3AD37B408 for ; Thu, 26 Jul 2001 10:14:53 -0700 (PDT) (envelope-from tlambert2@mindspring.com) Received: from mindspring.com (dialup-209.245.129.59.Dial1.SanJose1.Level3.net [209.245.129.59]) by falcon.mail.pas.earthlink.net (EL-8_9_3_3/8.9.3) with ESMTP id KAA19895; Thu, 26 Jul 2001 10:14:35 -0700 (PDT) Message-ID: <3B605020.9D2B1DB2@mindspring.com> Date: Thu, 26 Jul 2001 10:15:12 -0700 From: Terry Lambert Reply-To: tlambert2@mindspring.com X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: Julian Elischer Cc: Zhihui Zhang , Bosko Milekic , vishwanath pargaonkar , freebsd-hackers@FreeBSD.ORG Subject: Re: cluster size References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Julian Elischer wrote: > > no.. it has to do with the fact that it would be unwise > to make a cluster > 1 page size since we have no guarantee that > all drivers could handle breaking up a DMA if a cluster spanned 2 > physical address ranges. (they can handle a chain of discontinuous > mbufs but may assume that a single mbuf will have physically > contiguous data. Now since we cannot span a page boundary, > we should fit in exacly to get as much room as possible > and since (pagesize/3) is too small, the next possibility is (pagesize/2). FWIW: the way clusters work quarantees contiguity, based on the zone allocator being backed by contiguous regions in single pages. This is what Julian said, but it's less verbose... 8-). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message