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Date:      Sat, 6 Jul 2002 04:06:57 +0200
From:      Bernd Walter <ticso@cicely5.cicely.de>
To:        Darren Pilgrim <dmp@pantherdragon.org>
Cc:        freebsd-hackers@FreeBSD.ORG
Subject:   Re: How does swap work address spacewise?
Message-ID:  <20020706020656.GL48977@cicely5.cicely.de>
In-Reply-To: <3D2640A7.3EA2236B@pantherdragon.org>
References:  <20020705113532.GA11273@atrbg11.informatik.tu-muenchen.de> <20020705133515.GA295@HAL9000.wox.org> <20020705133837.GA513@HAL9000.wox.org> <20020705234126.GA12183@atrbg11.informatik.tu-muenchen.de> <3D2640A7.3EA2236B@pantherdragon.org>

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On Fri, Jul 05, 2002 at 05:58:15PM -0700, Darren Pilgrim wrote:
> If RAM + swap can be more than 4GB, how does FreeBSD address swap on a
> 32-bit machine?  Does the kernel internally use a wider address space

The same way it does on every partitition: using block numbers.
That way you can address 1TByte.
And you can have more than a single swap partition.
In reality managementstructures which have to be in kernel addressspace
is limiting swap before.

> with some kind of translation to 32-bit space for programs and hardware

Don't mix address space with ram and swap.
While you can have more than 4G swap you can't have more than 4G
addressspace.
But you can have multiple different 4G addressspaces - each process
with its own.

> that can't handle 64-bit addresses or does it not map swap into the

swap is logicaly mapped into address space, but not more than 4G
in a single one.

> address space at all, instead using it as a kind of "offline" storage
> for pages not in use?  Does the Alpha port handle swap the same way?

Yes - I see no reason to do it different.

-- 
B.Walter              COSMO-Project         http://www.cosmo-project.de
ticso@cicely.de         Usergroup           info@cosmo-project.de


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