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Date: Thu, 26 Sep 2002 17:27:59 +0200 (CEST)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@zip.com.au>
Subject: Re: [patch] 'sticky pages' support in the VM, futex-2.5.38-C5
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On Thu, 26 Sep 2002, Linus Torvalds wrote:

> This patch seems trivially broken by having two futexes on the same
> page.  When the first futex removes itself, it will clear the sticky
> bit, even though the other futex is still pinning the same page.

sigh. And we cannot even properly detect which unpin_page() was the last
unpinning of the page - there can be so many other reasons a page's count
is elevated. And keeping a page sticky forever is no solution either, the
number of sticky pages would increase significantly, causing real fork()
problems.

> Trust me, you'll have to use the page list approach.

yeah, will try that now. I'm a bit worried about the mandatory cross-CPU
TLB flushes though.

	Ingo

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