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From: stroyan@hpfcso.HP.COM (Mike Stroyan)
Newsgroups: comp.sys.hp
Subject: Re: Further question about iomap
Message-ID: <7370226@hpfcso.HP.COM>
Date: 4 Oct 90 02:53:05 GMT
References: <10647@pt.cs.cmu.edu>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Lines: 17

>A much better solution would be to iomap the device at someplace like
>0x40000000.  I'm afraid that trying to do that would force the kernel
>to give me a huge page table, if indeed it would work at all; so I
>have not tried it.
>
>Can anybody at HP provide a workable, efficient solution for mapping
>I/O devices without constraining subsequent use of malloc?

You are correct that mapping at a very high address will cause a very big
page table.  (Actually the call would usually fail because the address
is also limited by the configurable kernel parameter "shmmaxaddr".)
There are plans to allow very high addresses with a segmented page
table, and to make the default addresses very high.  Until those
changes make their way to a release and onto your disk, there is
no simple solution to choosing an address.

Mike Stroyan, mike_stroyan@fc.hp.com