Re: 1GB/2GB/3GB User Space Splitting Patch 2.6.8.1 (PSEUDO SPAM)

From: Timothy Miller (miller_at_techsource.com)
Date: 09/22/04

  • Next message: Florian Weimer: "Genesys and IEEE 1394 (was: Re: Genesys Logic and Kernel 2.4)" 
    Date:	Wed, 22 Sep 2004 16:22:55 -0400
To: Roland Dreier <roland@topspin.com>

    Roland Dreier wrote:
    > Timothy> My question is: Why can't we just shrink the kernel
    > Timothy> address space by that same amount, allowing the kernel
    > Timothy> address space plus the extra to fit into 1GB?
    >
    > If you have 1 GB of memory and want to map it all into the kernel's
    > address space and the kernel has only 1 GB of address space total,
    > then there is no room for anything else (such as address space to
    > ioremap memory-mapped peripherals or space for vmalloc allocations).
    > Therefore, if you want to have 1 GB of RAM mapped linearly into the
    > kernel's address space, you need strictly more than 1 GB of kernel
    > address space. In practice, 1.25 GB of kernel address space (a
    > PAGE_OFFSET value of 0xb0000000) works well with 1 GB of RAM. That's
    > what I run on my main desktop machine with 1 GB of RAM to avoid HIGHMEM.
    >
    > - Roland
    >
    >

    Ok, I understand now. I think. With 0xc0000000, you have 128M of
    highmem, right? Why do you add 256M to the kernel address space? Is
    there a further advantage to that?

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  • Next message: Florian Weimer: "Genesys and IEEE 1394 (was: Re: Genesys Logic and Kernel 2.4)"

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