Some odd behaviour of vmstat and vmtotal...

[gnn at freebsd.org]

Howdy,

In deploying 7.0 at work we were finding a persistent problem when
running "vmstat 1" on systems.  The problem shows up as a 10ms "pause"
in processing, usually packet stamping and forwarding by a user level
process.  This is due to the fact that vmstat calls the vmtotal()
routine which in turn does a whole lot of locking.  The vmtotal call
locks and walks the VM object list twice in a mark and sweep
operation.

So, the question is, "What is the right way to fix this?"  I could
remove the locking since the O_ACTIVE bit is not used by any other
routine besides vmtotal, but I'm not too happy about that.

The relevant code can be found in src/sys/vm/vm_meter.c in vmtotal().

Thoughts?

Best,
George