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From: John Von Essen <john@essenz.com>
Date: Fri, 1 Oct 2004 13:58:01 -0400
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Could there be some more elaboration on these memory issues.

 From the way you described it, it sounds like if you have two machines 
serving the same function with the same load, and one machine has 512Mb 
and the other has 2.5Gb, the one with more memory might be prone to be 
more problems.

Why is that? How do you tune the kernel to get around this?

-John

On Oct 1, 2004, at 12:36 PM, Doug Ambrisko wrote:

> How much memory are in these system?.  If you have 3G or more you end
> up with very little left for the kernel in the 2G space.  You can
> monitor how much space you have left by compile a debug kernel then
> as root:
> 	gdb -k kernel.debug /dev/mem
> 	print ((unsigned int)virtual_end)-((unsigned int)kernel_vm_end)
> This should probably be made into a sysctl so it can be montored
> better.
>
> If you only have a few meg. left it doesn't take many processes to
> fork etc. then you machine blows up.  The bge driver for example takes
> 4M each for the jumbo packet handling.  You can recover some of this
> memory via loader.conf tunables or bump KVA_PAGES in your kernel
> config file.  Still once this memory is put into the zone allocator
> (vmstat -z) in -stable it is gone from the system even if that bucket
> isn't fully used or needed :-(
>
> Ironically the more memory you put in a system the less you can do with
> the system!
>
> A lot of people are starting to run into this problem since large 
> memory
> machines are cheap.
>
> Doug A.