Tuning KVA_PAGES / kmem?

Stefan Bethke stb at lassitu.de
Tue Apr 20 08:17:35 PDT 2004

Am 20.04.2004 um 15:40 schrieb Ruslan Ermilov:

> On Tue, Apr 20, 2004 at 01:14:52PM +0200, Stefan Bethke wrote:
>> I dug through the archives, and I found some hints that with >>2 GB
>> RAM, the auto-tuning might produce undesirable results, so I might 
>> need
>> to tune KVA_PAGES to reserve more address space for the kernel, or
>> fiddle with VM_KMEM_SIZE_MAX, VM_KMEM_SIZE_SCALE, or some vm sysctls.
>> Can someone point me in the right direction?
> See sys/i386/conf/NOTES, when it talks about KVA_PAGES, for the
> starters.

Thanks, I already looked at that, but I'd be interested in some 
recommendations on which values for the various tunables would be 
better than the defaults. NOTES has this to say about KVA_PAGES:
# Change the size of the kernel virtual address space.  Due to
# constraints in loader(8) on i386, this must be a multiple of 4.
# 256 = 1 GB of kernel address space.  Increasing this also causes
# a reduction of the address space in user processes.  512 splits
# the 4GB cpu address space in half (2GB user, 2GB kernel).
options         KVA_PAGES=260

This neatly explains what changing the default will affect, but not 
really what to set it to given a certain amount of physical memory.

Certainly, there must be people running -current with 4 or 6 GB or RAM, 
and with some advice whcih parameters work for them?

Thanks again,

Stefan Bethke <stb at lassitu.de>   Fon +49 170 346 0140

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