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Date: Thu, 12 Jan 2012 21:23:52 -0600
From: Stephen Montgomery-Smith <stephen@missouri.edu>
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To: Garrett Cooper <yanegomi@gmail.com>
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Cc: Andre Goree <andre@drenet.info>, Doug Barton <dougb@freebsd.org>,
	freebsd-stable@freebsd.org, Rob Clark <rpclark@tds.net>
Subject: Re: GENERIC make buildkernel error / fails - posix_fadvise
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On 01/12/2012 09:11 PM, Garrett Cooper wrote:

> +1. And it's faster yet when you can run parallel copies of rm on
> different portions of the directory tree (e.g. xargs, find [..] -exec)
> as rm is O(n).

I have always wondered about that!  I thought that the main bottleneck 
in "rm -r" might be deleting directories which are not in the disk 
cache, which then have to be copied from the disk.  Copying two 
different parts of the disk into cache - well it has to be done one at a 
time whether the jobs asking for the copy of the disk are going 
concurrently or consecutively.

And perhaps two instances of "rm -r" acting on different parts of the 
hard drive will cause disk thrashing, so that they might even slow each 
other down.

But this is all guess work on my part.

If I am wrong, and "rm -r" does work faster when working in parallel on 
different parts, then why doesn't someone write the "rm" command to fork 
copies of itself that work on different parts of large trees?

Stephen