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Date: Tue, 12 Nov 2002 10:11:46 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: Ingo Molnar <mingo@elte.hu>
To: Jamie Lokier <lk@tantalophile.demon.co.uk>
Cc: "Perez-Gonzalez, Inaky" <inaky.perez-gonzalez@intel.com>,
       Rusty Russell <rusty@rustcorp.com.au>,
       "'Mark Mielke'" <mark@mark.mielke.cc>, <linux-kernel@vger.kernel.org>
Subject: Re: Users locking memory using futexes
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On Tue, 12 Nov 2002, Jamie Lokier wrote:

> It would be nice if the futex waitqueues could be re-hashed against swap
> entries when pages are swapped out, somehow, but this sounds hard.

yes it sounds hard (and somewhat expensive). The simple solution would be
to hash against the pte address, which is an invariant over swapout - but
that breaks inter-process futexes. The hard way would be to rehash the
futex at the pte address upon swapout, and rehash it with the new physical
page upon swapin. The pte chain case has to be careful, and rehashing
should only be done when the physical page is truly unmapped even in the
last process context.

but this should indeed solve the page lockdown problem.

	Ingo

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