linux-kernel - Re: Summary of resource management discussion

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Message-Id: <20070316142356.3b9a5597.pj@sgi.com>
Date:	Fri, 16 Mar 2007 14:23:56 -0700
From:	Paul Jackson <pj@....com>
To:	Herbert Poetzl <herbert@...hfloor.at>
Cc:	vatsa@...ibm.com, menage@...gle.com,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	xemul@...ru, ebiederm@...ssion.com, winget@...gle.com,
	containers@...ts.osdl.org, akpm@...ux-foundation.org
Subject: Re: Summary of resource management discussion

Herbert wrote:
> looks good to me, except for the potential issue with
> the double indirection introducing too much overhear

It's not the indirection count that I worry about.

It's the scalability of the locking.  We must avoid as
much as possible adding any global locks on key code paths.
This means:
 1) be reluctant to add them to fork/exit
 2) just RCU locks on per-job (or finer grain) data when on
	the normal page allocation path
 3) nothing outside the current task context for the normal
	task scheduling code path.

A global lock on the wrong code path is fatal for scaling
big NUMA boxes.

... now whether or not that is an issue here, I don't claim
to know.   I'm just worried that it could be.

Atomic data, such as global counters, is just as bad.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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