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From: John Dyson <dyson@dyson.iquest.net>
Message-Id: <199610021740.MAA01329@dyson.iquest.net>
Subject: Re: vnode and cluster read-ahead
To: dfr@render.com (Doug Rabson)
Date: Wed, 2 Oct 1996 12:40:10 -0500 (EST)
Cc: dyson@freebsd.org, phk@critter.tfs.com, heo@cslsun10.sogang.ac.kr,
        freebsd-hackers@freebsd.org, freebsd-fs@freebsd.org
In-Reply-To: <Pine.BSF.3.95.961002181522.10204N-100000@minnow.render.com> from "Doug Rabson" at Oct 2, 96 06:21:13 pm
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> 
> You could maintain a number of 'pending readahead' structures indexed by
> vnode and block number.  Each call to cluster_read would check for a
> pending readahead by hashing.  For efficiency, keep a pointer to the last
> readahead structure used by cluster_read in the vnode in place of the
> existing in-vnode readahead data.  Should be no slower than the current
> system for single process reads and it saves 4 bytes per vnode :-).
> 
Pretty cool idea.  I am remembering now that this deficiency in our read
ahead code is well known.  This might be something really good for 2.3 or
3.1 :-).  (Unless someone else wants to implement it -- hint hint :-)).

John