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From: John Dyson <dyson@dyson.iquest.net>
Message-Id: <199607121557.KAA02358@dyson.iquest.net>
Subject: Re: kernel malloc question
To: fqueries@jraynard.demon.co.uk (James Raynard)
Date: Fri, 12 Jul 1996 10:57:14 -0500 (EST)
Cc: jpbelang@crim.ca, freebsd-questions@freebsd.org
In-Reply-To: <199607102232.WAA04010@jraynard.demon.co.uk> from "James Raynard" at Jul 10, 96 10:32:41 pm
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> 
> > This is a beginner device driver question:
> > 	The kernel malloc returns physical memory (non swappable), right?
> 
> Yes, all memory used by the kernel is non-pageable, although changing
> this is on the wish-list.
> 
Well, actually, you can use kmem_alloc_pageable to get pageable kernel
memory.  You have to be careful to have process context when page faulting.

For a complete implementation of how to do kernel pageable memory, I
refer you to the sys_pipe.c in -current.  The pipe buffers are pageable.
Also, the arg list temporary space in kern_exec is also pageable.

You are absolutely right about the malloc() stuff being non-pageable
though.

Sorry that I have not responded sooner, I read my mail at work, file it
and am sometimes rude and forget it it :-(.  I apologize.

John