linux-kernel - Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

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Message-ID: <20070719012848.GO11115@waste.org>
Date:	Wed, 18 Jul 2007 20:28:48 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Rene Herman <rene.herman@...il.com>
Cc:	Andrea Arcangeli <andrea@...e.de>, Ray Lee <ray-lk@...rabbit.org>,
	Bodo Eggert <7eggert@....de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

On Thu, Jul 19, 2007 at 02:48:37AM +0200, Rene Herman wrote:
> On 07/19/2007 02:41 AM, Matt Mackall wrote:
> 
> >On Thu, Jul 19, 2007 at 02:15:39AM +0200, Andrea Arcangeli wrote:
> 
> >>Using kmalloc(8k) instead of alloc_page() doesn't sound a too big deal
> >>and that will solve the problem.
> >
> >How do you figure?
> >
> >If you're saying that soft pages helps our 8k stack allocations, it
> >doesn't. The memory overhead of soft pages will be higher (5-15%,
> >mostly due to file tails in pagecache) than the level at which 8k
> >stacks currently run into trouble (1-2% free?).
> >
> >Not helpful.
> 
> With tail-packing it is.

Tail packing is a whole new can of worms. Especially as it's very
likely to make performance suffer on small files (the common case).

On the other hand, if someone can demonstrate that tail-packed page
cache doesn't suck, we should put it in mainline pronto. The poor
architectures that are stuck with real 64k pages are sure to
appreciate it.

-- 
Mathematics is the supreme nostalgia of our time.
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