Message-ID: <4011B586.1090101@cyberone.com.au>
Date: Sat, 24 Jan 2004 11:00:06 +1100
From: Nick Piggin <piggin@cyberone.com.au>
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To: Randy Appleton <rappleto@nmu.edu>
CC: Bill Davidsen <davidsen@tmr.com>, linux-kernel@vger.kernel.org
Subject: Re: Unneeded Code Found??
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Randy Appleton wrote:

> Nick Piggin wrote: 


>
>> Yes it gets used.
>>
>> I think its a lot more common with direct io and when you have lots of
>> processes.
>
>
> I'm not arguing, but how do you know this?  I'm trying to convince 
> myself that the code is used, and at least on my system
> a few days of general use, followed by heavy parallel compiles, 
> doesn't use the code even once.
>
> I have not tested direct I/O.  Otherwise it looks unused.
>

Because I have seen it - I have instrumented it.

Your usage patterns are pretty tame actually. I remember having 100 
processes
randomly reading from the same part of the disk was one of my test cases.
You need direct IO otherwise everything ends up in pagecache.

I haven't seen workloads where it gets used a lot, but that doesn't mean 
they
don't exist, and I've never seen the code cause any problems, so there is no
need to make any trade offs by removing it.


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