linux-kernel - Re: Does process need to have a kernel-side stack all the time?

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Message-ID: <20080416124728.GA5050@elte.hu>
Date:	Wed, 16 Apr 2008 14:47:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Does process need to have a kernel-side stack all the time?


* Andi Kleen <andi@...stfloor.org> wrote:

> Denys Vlasenko <vda.linux@...glemail.com> writes:
> 
> > A lot of effort went into minimizing of stack usage.
> > If I understand it correctly, one of the reasons for this
> > was to be efficient and not have lots of pages
> > used for stacks when we have a lot of threads
> > (tens of thousands).
> 
> Actually the real reason the 4K stacks were introduced IIRC was that 
> the VM is not very good at allocation of order > 0 pages and that only 
> using order 0 and not order 1 in normal operation prevented some 
> stalls.

no, the primary motivation Arjan and me started working on 4K stacks and 
implemented it was what Denys mentioned: i had a testcase that ran 
50,000 threads before it ran out of memory - i wanted it to run 100,000 
threads. The improved order-0 behavior was just icing on the cake.

	Ingo
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