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From: John Dyson <dyson@dyson.iquest.net>
Message-Id: <199610021439.JAA00980@dyson.iquest.net>
Subject: Re: vnode and cluster read-ahead
To: heo@cslsun10.sogang.ac.kr (Heo Sung-Gwan)
Date: Wed, 2 Oct 1996 09:39:42 -0500 (EST)
Cc: freebsd-hackers@freebsd.org, freebsd-fs@freebsd.org
In-Reply-To: <Pine.SUN.3.93.961002231449.5132A-100000@cslsun10> from "Heo Sung-Gwan" at Oct 2, 96 11:17:03 pm
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> When a file is open serveral times simultaneously cluster read-ahead 
> buffer cache using vnode seem to have some problems.
>                              
You are right.

> As a process A reads a file F *sequentially* the fields(v_maxra, v_ralen, etc) of the vnode of F increases. As a result read-ahead of next cluster happens.
> But when a process B opens F and reads it the values of the fields are 
> changed. So the process A's read-ahead is disturbed whenever process B is 
> rescheduled.
> 
> I think the fields for read-ahead must be in struct file rather than vnode.
> There exists one vnode for a file but a file may be open serveral times. 
> 
That is closer to correct.  I am not sure that the struct file is correct
either, but I think that you are on the right track.

John