Freebsd 8.0 kmem map too small

[Pawel Jakub Dawidek]

On Wed, May 12, 2010 at 03:36:59PM +0300, Alexander V. Ribchansky wrote:
> I apply you patch on today's STABLE. with 2Gb of ram
> m.kmem_size_max: 1073741824
> vm.kmem_size_min: 0
> vm.kmem_size: 1073741824
> 
> hw.physmem: 2125430784
> hw.usermem: 1291554816
> hw.realmem: 2146959360
> 
> vfs.zfs.arc_max: 268435456
> 
> it survive two sequent buildworld & buildkernel. Wired memory is 791M. 
> Without UMA Wired memory was around 500M on THE SAME settings.
> Could you please explain as for nOOb, what we get with UMA, and why it 
> uses MORE Wired memory? Is it for better perfomance or for what? [...]

Well, UMA doesn't really free memory until it is asked by the pageout
daemon when we are running out of physical pages.

In general UMA allows to achive better performance than regular
malloc(9), but I wasn't the one who decided to switch to UMA - it was
Kip Macy. I'm not sure what tests he performed and what performance
benefits he measured.

> [...] What is 
> your recomended tuning for i386 FreeBSD-8 on 2Gb ram typical desktop?

Well, I was running i386 kernel on my laptop with 2.5GB for a few years
without single 'kmem_map too small' panic. I had KVA_PAGES set to 512 in
my kernel config and vm.kmem_size set to around 1GB (the biggest
possible value I could find).

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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