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Kernel/Userland Mem-Space Tuning (1/3 on IA32)



David G. Lawrence wrote:

>>>>sure about the exakt syntax but I know someone can change the half by 
>>>>half parity towards 1 to 3 in
>>>>XP). I'm not sure whether FreeBSD divides kernel/userland address space 
>>>>this way, I know Linux and
>>>>Windows does and on Windows we changed this (not yet on Linux and not 
>>>>yet on our FreeBSD machines
>>>>(OS version >5.0, mostly FreeBSD 5.3-R or 5.4-PRERELEASE).
>>>>
>>>>Any help is appreciated.
>>>>  
>>>>
>>>>        
>>>>
>>> FreeBSD divides the 32bit virtual address space with 1GB for the kernel
>>>and 3GB for user processes. This can be changed with some kernel compile-
>>>time constants (primarily KVA_PAGES, however NKPT may also need to be
>>>increased if the kernel address space is increased).
>>>      
>>>
>...
>  
>
>>Dear David.
>>Thank you very much.
>>I assumed FreeBSD do the same like Linux, but don't obviously.
>>
>>I found a lot of tweaking kernel parameters,
>>KVA_PAGES
>>VM_KMEM_SIZE_SCALE
>>VM_KMEM_SIZE_MAX
>>VM_KMEM_SIZE
>>    
>>
>
>   The last three are not related to the address space division and you
>should not change those under normal circumstance.
>
>  
>
>>Reading some comments  in sys/kern/kern_malloc.c make be a bit confused, 
>>I do not know much about kernel's interna.
>>
>>It is nice to hear that FreeBSD do a 1/3 division, I expected a 2/2 
>>division like Linux does. So no need for anything changing.
>>    
>>
>
>   It's a 1:4 ratio.
>  
>

Sorry, I meant 1GB kernel, 3GB userland or 2GB kernel, 2GB userland, not 
the divisor or
mathematical ratio, sorry for this unprecise.

> 
>  
>
>>Can someone please explain NKPT? I'm simply curious, didn't found a 
>>satisfying answer via google, but a lot of source code with this in ...
>>    
>>
>
>   It's the number of page table pages that are assigned to the kernel
>address space. Each page maps 4MB, so 256 (the default) provides for
>1GB of kernel virtual address space, leaving 3GB for user space.
>  
>
Many thanks, that helped a lot!

Oliver


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