Subject: Re: VM_TOPDOWN
To: Quentin Garnier <>
From: Andrew Brown <>
List: port-amd64
Date: 01/02/2006 14:22:34
On Mon, Jan 02, 2006 at 03:00:24PM +0100, Quentin Garnier wrote:
>I've just noticed that VM_TOPDOWN isn't used on amd64.  Is it an
>overlook or is there a compelling reason for it?

no specific reason for it -- it's mainly just up to the portmaster.

>In any case, it seems to jsut work.  The patch I'm including also adds
>code to make netbsd32 binaries use the topdown layout, and sync a few
>VM parameters with their i386 counterparts.

you should check with the portmaster.  i don't know anything about the
vm layour on amd64, so i can't say if it's a win or not.  on the alpha
(another 64 bit arch), for example, it's not, since the stack sits
roughly in the middle of the user's vm space, and doing topdown would
incur more tlb entries or something.  i forget what.

>I'd like to commit it unless someone objects.  Notice the huge available
>VM space for netbsd32 binaries on an amd64 system:
>% /mnt/netbsd32/bin/sh
>$ /../usr/bin/pmap
>0000000008048000    104K read/exec         /mnt/netbsd32 -?-
>0000000008062000      4K read/write          [ anon ]
>0000000008063000     24K read/write          [ anon ]
>00000000FBEFF000      4K read/write          [ anon ]
>00000000FBF00000    724K read/exec         /mnt/netbsd32 -?-

much like the regular i386 space.  :)

>amd64 binaries look like this:
>$ pmap
>0000000000400000    116K read/exec         / -?-
>000000000051C000     16K read/write        / -?-
>0000000000520000     32K read/write          [ anon ]
>00007F7FFD800000    800K read/exec         / -?-
>00007F7FFD8C8000   1024K                   / -?-
>00007F7FFD9C8000    116K read/write        / -?-
>00007F7FFD9E5000     68K read/write          [ anon ]

looks fine to me, but i'm not the expert.  :)

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