linux-kernel - Re: boot cgroup questions

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Date:	Thu, 13 Mar 2008 02:12:53 -0500
From:	Paul Jackson <pj@....com>
To:	Max Krasnyanskiy <maxk@...lcomm.com>
Cc:	menage@...gle.com, mingo@...e.hu, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org
Subject: Re: boot cgroup questions

> How about we add support for sym links to the cgroup fs ?

Still pollutes the primary cpuset name space ... you have all
the directories X, X/A, and X/B as well as the symlinks A and B.

Symlinks allow for one path that needs to be 'aliased' to another,
but they are a one-way map; without an exhaustive search of the
potential namespace, one can't invert them, or determine if they
can't be inverted.

Tools have to constantly make heuristic decisions whether to
default to dereferencing the symlink, or not, and often have to
provide alternatives for the non-default choice.

They are a pain in the backside even if designed in and expected
up front.

If added as critical structure after the fact, something breaks,
pretty much for sure.

For one minor example, code I've probably buried someplace that
does "find /dev/cpuset -type d" to find all cpusets would break.

Or the one-line /sbin/cpuset_release_agent script:
	rmdir /dev/cpuset/$1
is broken -- fails to clean-up associated symlinks, and can't
avoid race conditions if it tries to add code to do that.

> Crazy idea.

Agreed ;)

But nice picture ;).

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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