[lug] kupdate and stalls

[Tim Fredrick]

Hello,
   We have a 4-CPU 500MHz Xeon Dell Poweredge here with a bunch (about 256
accounts and about 32 active logins) here that has started behaving
badly.  That is, 2 or 3 times in a 30-minute period it will stall for a
few seconds.  I took a look at "top" and "xosview" and what happens
is the CPU LOAD goes high up to as much as 20.  Yet we see less activity
on the individual CPU's, no swap usage, no disk activity, and a lessening
of process activity.  In terms of process activity, the USR processes
nearly disappear while the SYS processes diminish in activity.
   top shows that during this time, we're running "kupdate" and "kupdate"

    2 root       3   0     0    0     0 DW      0  7.7  0.0  15:40 kflushd
    3 root       1   0     0    0     0 DW      0  5.8  0.0  34:12 kupdate

along with an expected mix of user processes.  Can someone tell me what
these two processes which are part of the kernel do?   Our system's
set is currently:

	Redhat 6.1
	Kernel 2.2.14 SMP
	2GB RAM (1.8 show up as being used on cat /proc/meminfo)
	OS and swap space on RAID disk, user files on separate RAID disk

Can someone advise how I might further figure out what's causing these
nasty stalls?  Would upgrading the Redhat version or kernel be a way out
of this?  How about calling Scully and Mulder?

   Thanks in advance,  --Tim (fredrick at acd.ucar.edu)
                         NCAR/ACD Computer Systems Administration