linux-kernel - Re: [PATCH] jump_label: jump

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Date:	Fri, 02 Dec 2011 13:53:27 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	rostedt@...dmis.org
Subject: Re: [PATCH] jump_label: jump_label for boot options.

On Fri, 2011-12-02 at 13:45 +0100, Johannes Weiner wrote:
> On Fri, Dec 02, 2011 at 10:24:10AM +0100, Peter Zijlstra wrote:
> > On Fri, 2011-12-02 at 09:22 +0900, KAMEZAWA Hiroyuki wrote:
> > > 
> > > Yes, that's an idea. But we also have another stupid shadow swap accounting
> > > table.  This can be disabled at boot, too. 
> > 
> > Bah I thought it was just the page frame thing, hnaz any plans to kill
> > this swap array as well?
> 
> I haven't looked at the swap accounting at all yet, sorry.  But where
> did this discussion go all of a sudden? :-)
> 
> That array is not allocated at all when the memory controller is
> disabled at boot-time.
> 
> Rather, we have those mem_cgroup_disabled() conditionals everytime we
> enter the memory controller from the VM and the idea is to patch them
> out during boot, since you can not re-enable the thing anyway.

Yeah, but without those arrays you could.. this boot time switch really
is a wart and if you don't have the shadow page frame and shadow swap
accounting muck stuff you could runtime flip all this..

I've no objection to using jump_labels fwiw, we're looking to do the
same with the cpu controller for the nr_cgroups == 0 case. But boot time
stuff just doesn't make sense to me.

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