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Old 09-13-2007, 01:32 PM   #1
jhwilliams
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high/low zones in kernel mmu for x86_64


For x86_64, since it has a larger address space than x86, is ZONE_HIGHMEM even relevant? where does ZONE_NORMAL end on x86_64 ?

I have 3GB ram on my system and

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free -ml
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High: 0
 
Old 09-13-2007, 02:27 PM   #2
osor
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As of 2.6.19 ZONE_HIGHMEM is no longer in the kernel for x86_64. Prior to that, it was in the kernel but never used by such archs. Now it has been removed with conditional compilation, namely by using CONFIG_HIGHMEM which is not even an option except for the following archs: i386, powerpc, m32r, mips, um, frv, xtensa, sparc, and ppc.
 
Old 09-13-2007, 03:30 PM   #3
jhwilliams
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Ah yes, neat.

A related question: On x86, I understand that 896MB = 1024MB - 128MB, right? (128MB being kernel space? ) I had thought that the address space on any 32-bit machine was 4GB, as opposed to 1GB as it appears above?

Last edited by jhwilliams; 09-13-2007 at 03:45 PM.
 
Old 09-13-2007, 04:46 PM   #4
jhwilliams
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In reference to my last post, above - I found this article which helps explain it, somewhat well. As far as I'm concerned in the end, "You don't want to know, dude. Just run an x86_64."

Last edited by jhwilliams; 09-13-2007 at 04:52 PM.
 
  


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