linux-kernel - Re: x86: 4kstacks default

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Date:	Sun, 20 Apr 2008 15:33:17 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Daniel Hazelton <dhazelton@...er.net>,
	Adrian Bunk <bunk@...nel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86: 4kstacks default

On Sun, 20 Apr 2008 22:01:46 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> 
> 
> > These are real customer workloads; java based "many things going
> > on" at a time showed several thousands of threads fin the system (a
> > dozen or two per request, multiplied by the number of outstanding
> > connections) for *real customers*.
> 
> Several thousands or 50k? Several thousands sounds large, but not
> entirely unreasonable, but it is far from 50k.

it is you who keeps putting up the 50k argument.
What I'm talking about is in the 10k to 20k range; and that is actual workloads
by real customers.
> 
> > That you don't take that serious, fair, you can take serious
> > whatever you want.
> 
> No I don't take 50k threads on 32bit serious. And I hope you do not
> either.

[ removed a bunch of stuff about 50k again ]

> 
> > was the observation that fragmentation is fundamentally unsolvable.
> 
> Where was that observation? 

it was in the commit message from me you quoted, and was rather widely discussed at the time.
It's also basic math; the Linux VM gets to deal with both short and long lasting allocations;
no matter how hard you try to get some degree of fragmentation; especially due to the
15:1 acceleration you get due to the lowmem issue.

And before you say "you should use 64 bit on such machines"; I would love it if more people used 64 bit linux.
Sadly the adoption rate of that is not very good still.... by far ;(

> 
> > Yes 2.4 sucked a lot more than 2.6 does. But even 2.6 will (and
> > does) have fragmentation issues. We don't have effective physical
> > address based reclaim yet for higher order allocs.
> 
> I don't see any evidence that there are serious order 1 fragmentation 
> issues on 2.6. 

I assume you're not asking me to give you customer confidential data from a previous job in public ;)

>If you have any please post it.

just like you're posting the evidence that 4k stacks overflows?

Google scores:

1-order allocation failed		54000 pages
do_IRQ: stack overflow			4560 pages


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