Sudden Reboots

[Doug Ambrisko]

Jim Durham writes:
| I have had this problem now with at least 3 FreeBSD servers over a period of 
| about 2 years. I had put it down to some hardware problem but it seems to be 
| too much of a coincidence with 3 different machines doing the same thing.
| 
| The first time was when I put 4.5-RELEASE on a brand new Dell Poweredge 2650. 
| I ran it on the bench for a week or so, then decided all was well and put it 
| in the server rack and started doing the company's email service on it. After 
| a few weeks, it suddenly would 'reboot' for no apparent reason. No log 
| entries, nothing at all except the usual stuff in /var/log/messages about '/ 
| was not unmounted correctly', etc. Just like you had pulled the power plug.

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.