From owner-freebsd-hackers Fri May 16 07:26:39 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.5/8.8.5) id HAA00480 for hackers-outgoing; Fri, 16 May 1997 07:26:39 -0700 (PDT) Received: from dyson.iquest.net (dyson.iquest.net [198.70.144.127]) by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id HAA00475 for ; Fri, 16 May 1997 07:26:34 -0700 (PDT) Received: (from root@localhost) by dyson.iquest.net (8.8.5/8.6.9) id JAA01426; Fri, 16 May 1997 09:26:24 -0500 (EST) From: "John S. Dyson" Message-Id: <199705161426.JAA01426@dyson.iquest.net> Subject: Re: mmap() In-Reply-To: <337C3FAE.4295@westongold.com> from James Mansion at "May 16, 97 12:06:22 pm" To: james@westongold.com (James Mansion) Date: Fri, 16 May 1997 09:26:24 -0500 (EST) Cc: freebsd-hackers@FreeBSD.ORG Reply-To: dyson@FreeBSD.ORG X-Mailer: ELM [version 2.4ME+ PL31 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > Terry Lambert wrote: > > > > > > Maybe you can convince John Dyson that coding this would be fun (it > > > > might even actually *be* fun 8-)), and then checking the degradation > > > > this causes in the general case to see if it's unacceptably high for > > > > your special case. > > > > > > I can't see that this would be a high cost. You'd only tell the real > > > benefit on a loaded system anyway. > > > > It would have a cost higher than not doing it (ie: non-zero). Using > > mmap() and then doing sequential I/O is probably a very limited market, > Okay!!! Firstly, the FFS FS dependent VOP_GETPAGES does do read-aheads iff the object is marked with MADV_SEQUENTIAL. Secondly, it would be fairly easy to detect sequential behavior automatically. Right now, there are much bigger fish to fry!!! :-) (The reason that it is in the FS dependent code, is that it is only optional that one uses the cluster read ahead code on a per filesystem basis.) It is likely that the FFS dependent VOP_GETPAGES code will work with other filesystem types (perhaps with minor mods.) John