Date:	Thu, 30 Apr 2009 12:03:16 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Yuriy Lalym <ylalym@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ltt-dev@...ts.casi.polymtl.ca, Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>, thomas.pi@...or.dea,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [ltt-dev] [PATCH] Fix dirty page accounting in
	redirty_page_for_writepage()

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > * Ingo Molnar (mingo@...e.hu) wrote:
> > > 
> > > * Christoph Lameter <cl@...ux.com> wrote:
> > > 
> > > > On Wed, 29 Apr 2009, Mathieu Desnoyers wrote:
> > > > 
> > > > > to have a good look at the memory accounting code. We could 
> > > > > probably benefit of Christoph Lameter's cpu ops (using segment 
> > > > > registers to address per-cpu variables with atomic inc/dec) in 
> > > > > there. Or at least removing interrupt disabling by using preempt 
> > > > > disable and local_t variables for the per-cpu counters could 
> > > > > bring some benefit.
> > > > 
> > > > Guess we are ready for atomic per cpu ops now that the new per cpu 
> > > > allocator is in? Segment register issues with the PDA are also 
> > > > solved right?
> > > 
> > > it's all done, implemented and upstream already. You are a bit late 
> > > to the party ;-)
> > > 
> > > 	Ingo
> > 
> > Or way too early, depending on the point of view. :-)
> > 
> > e.g.
> > http://lkml.org/lkml/2008/5/30/3
> > 
> > I think Christoph deserves credits for pioneering this area with fresh
> > ideas.
> 
> Ok, i didnt want to go there - but let me correct this version of 
> history.
> 
> Christoph's zero-based x86 percpu patches were incomplete and never 
> worked reliably - Christoph unfortunately never addressed the 
> bugs/crashes i reported. (and Mike Travis and me injected quite a 
> bit of testing into it) There were two failed attempts to productize 
> them and the patches just bitrotted for more than a year.
> 
> Tejun on the other hand fixed those problems (four of Christoph's 
> patches survived more or less and were credited to Christoph) and 
> did more than 50 highly delicate patches of far larger complexity to 
> solve the _whole_ problem range - within a two months timeframe.
> 
> Ideas and half-done patches covering <10% of the work needed are not 
> enough. Being able to implement it and productize it is the real 
> deal, in my book.
> 
> Thanks goes to Christoph (and Rusty) for coming up with the idea, 
> but it would be manifestly unfair to not send 90% of the kudos to 
> Tejun for turning it all into reality and fixing all the other 
> problems and redesigning almost all the x86 percpu code in the 
> process! ;-)
> 

Then thanks to Christoph, Rusty and to Tejun for the respective effort
they did. My goal is surely only to recognise their respective credit.

Mathieu

> 	Ingo
> 
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> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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