Hello. I'm running a series of machines, both Xen VM machines and
machines running on
bare metal, and I notice that on my systems running NetBSD-9.99.77, vmstat -s
shows that
local-cpu page allocations are never available on the xen VM's, see below.
Yet, on machines
running on bare metal, local-cpu page allocations are often available, which is
what I would
expect. A hand inspection of the sys/uvm kernel sources leads me to suspect
this condition
still exists under today's -current and the -10 branch of the source tree. The
Xen VM I'm
showing is configured with 2 VCPU's and the bare metal example I'm showing has
4 CPUs. My
questions are as follows:
1. What does the local-cpu stat actually reference? Is it counting the number
of times a CPU
requested a page of memory and a page was available from the local per-cpu free
list?
2. What's special about Xen that makes no local-cpu allocations available?
(For the record, I see this behavior on all the 9.99.77 Xen machines I have
running.)
As a point of reference, under NetBSD-9.2, local-cpu allocations are available
much of the time under Xen.
3. Is this a design decision or is it an actual bug?
-thanks
-Brian
<vmstat-s output from a Xen VM machine>
2908605631 pagealloc desired color avail
242456994 pagealloc desired color not avail
0 pagealloc local cpu avail
3151062625 pagealloc local cpu not avail
18763 faults with no memory
<vmstat -s output on actual bare metal hardware>
355234902 pagealloc desired color avail
250631 pagealloc desired color not avail
310440195 pagealloc local cpu avail
45045338 pagealloc local cpu not avail
0 faults with no memory
