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    SubjectRe: [PATCH] 1-2-3 GB
    On Sat, Jan 12, 2002 at 12:26:35PM -0500, Albert D. Cahalan wrote:
    > Andrea Arcangeli writes:
    > > On Fri, Jan 11, 2002 at 11:32:37PM -0800, H. Peter Anvin wrote:
    > >> By author: rwhron@earthlink.net
    >
    > >>> --- linux.aa2/arch/i386/config.in Fri Jan 11 20:57:58 2002
    > >>> +++ linux/arch/i386/config.in Fri Jan 11 22:20:32 2002
    > >>> @@ -169,7 +169,11 @@
    > >>> if [ "$CONFIG_HIGHMEM64G" = "y" ]; then
    > >>> define_bool CONFIG_X86_PAE y
    > >>> else
    > >>> - bool '3.5GB user address space' CONFIG_05GB
    > >>> + choice 'Maximum Virtual Memory' \
    > >>> + "3GB CONFIG_1GB \
    > >>> + 2GB CONFIG_2GB \
    > >>> + 1GB CONFIG_3GB \
    > >>> + 05GB CONFIG_05GB" 3GB
    ^^ this should be 3.5GB btw
    > >>> fi
    > >>
    > >> Calling this "Maximum Virtual Memory" is misleading at best. This is
    > >> best described as "kernel:user split" (3:1, 2:2, 1:3, 3.5:0.5);
    > >> "maximum virtual memory" sounds to me a lot like the opposite of what
    > >> your parameter is.
    > >
    > > actually it is really max virtual memory.. but from the user point of
    > > view, user is supposed to care about the virtual memory he can manage,
    > > not about what the kernel will do with the rest. So if the user wants
    > > 3GB of virtual memory available to each task he will select 3GB. I
    > > really don't mind if you want to change it from the kernel point of
    > > view, but given it's the user who's supposed to compile it, also the
    > > current patch looks good enough to me.
    >
    > The numbers are wrong anyway, because of vmalloc() and PCI space.
    > The PCI space is motherboard-dependent AFAIK, but you could at
    > least account for the 128 MB vmalloc() area:

    looks dirty, the size of the kernel direct mapping is mainly in function
    of #defines that can be changed freely, they're not constant in function
    of CONFIG_1G etc.. and it changes also in function of smp/up/4G/64G
    options. The 3GB/2GB/1GB/3.5GB visible into the menuconfig are exact
    instead. So I wouldn't mention inprecise stuff that can changed under
    us (and the exact size of the kernel direct mapping doesn't matter to
    the user anyways I think [and if it matters I think it means he's
    skilled enough to know about vmalloc space ;) ]).

    >
    > user virtual space / non-kmap physical memory
    >
    > 3584/384
    > 3072/896
    > 2048/1920
    > 1024/2944 (sure this works, even for syscalls w/ bad pointers?)
    > 512/3456 (sure this works, even for syscalls w/ bad pointers?)

    Andrea
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