linux-kernel - Re: copy_from_user / copy_to

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Date:	Tue, 17 Oct 2006 07:58:30 -0300
From:	"Horst H. von Brand" <vonbrand@....utfsm.cl>
To:	mfbaustx <mfbaustx@...il.com>
cc:	"Oliver Neukum" <oliver@...kum.org>, linux-kernel@...r.kernel.org
Subject: Re: copy_from_user / copy_to_user with no swap space 

mfbaustx <mfbaustx@...il.com> wrote:
> >>> No. Your code may be only partially paged into RAM.
> >>> The same can happen for any mmaped data.

> That's what I thought I read.  But then my question is:  with
> on-demand  paging, is it possible to have two processes partially
> paged?

Why shouldn't they be? The whole idea is having just /parts/ (hopefully the
ones in active use) in memory.

>         Surely, it  MUST be the case that any processes with
> overlapping logical address  spaces must be paged coherently.

I don't know what this is supposed to mean...

>                                                                So,
> while on-demand "paging-in" allows  for partial paging of a process,
> is it the case that, on a context switch,  the user-space PTE's are
> completely erased (so that you get page-faults  and can then on-demand
> page them in...)?

Each process has its own page tables, they don't get in each others
hair. And the page tables precisely manage making several processes get
access to the /same/ logical addresses, but at /different/ physical
addresses.
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
Departamento de Informatica                    Fono: +56 32 2654431
Universidad Tecnica Federico Santa Maria             +56 32 2654239
Casilla 110-V, Valparaiso, Chile               Fax:  +56 32 2797513
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