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Date: Tue, 29 Jan 2002 13:08:12 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: Oliver Xymoron <oxymoron@waste.org>
cc: Daniel Phillips <phillips@bonn-fries.net>,
        Rik van Riel <riel@conectiva.com.br>,
        Josh MacDonald <jmacd@CS.Berkeley.EDU>,
        linux-kernel <linux-kernel@vger.kernel.org>,
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Subject: Re: Note describing poor dcache utilization under high memory pressure
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On Tue, 29 Jan 2002, Oliver Xymoron wrote:
>
> fork:
>   detach page tables from parent

 - leave the option ot just mark them read-only on architectures that
   support it (ie x86, I think alpha does this too).

>   retain pointer to "backing page tables" in parent and child
>   update use count in page tables

You want to copy the top-level page table directory (with the "present
bit" disabled or something), not just retain a pointer to it. Otherwise
you just get really confused after two fork() calls, where you can have
multiple "backing page tables".

>   "prefault" tables for current stack and instruction pages in both parent
>     and child

Don't unconditionally prefault. There are many potentially useful things
that do _not_ want to do this, for example snapshot creation.

So the generic "do_fork()" thing should _not_ do prefaulting, although
"sys_fork()"  may well choose to do it.

			Linus

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