linux-kernel - Re: A little coding style nugget of joy

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Message-ID: <20070919213010.GG18707@one.firstfloor.org>
Date:	Wed, 19 Sep 2007 23:30:10 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andy Lutomirski <luto@...ealbox.com>
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	kernel1@...erdogtech.com
Subject: Re: A little coding style nugget of joy

> This is a terrible assumption in general (i.e. if filesize % blocksize 
> is close to uniformly distributed).  If you remove one byte and the data 
> is stored with blocksize B, then you either save zero bytes with 
> probability 1-1/B or you save B bytes with probability 1/B.  The 
> expected number of bytes saved is B*1/B=1.  Since expectation is linear, 
> if you remove x bytes, the expected number of bytes saved is x (even if 
> there is more than one byte removed per file).

You didn't calculate the probability of actually saving a full block 
or not (that's the only thing that matters). I assumed it's relatively
small and can be ignored in practice since the amount of end white
space is negligible compared to total file size.

-Andi
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