Re: snmp oid for memory usage, vmstat -i and others

Victor Gamov wrote:
> Hi All
> 
> Some questions about bsnmpd.
> 
> Is it possible to get memory usage via bsnmpd?  When I tried to get
> something like "snmpget hrStorageDescr.1 hrStorageAllocationUnits.1
> hrStorageSize.1 hrStorageUsed.1" then I've got this values:
> 
> =====
> HOST-RESOURCES-MIB::hrStorageDescr.1 = STRING: Real Memory Metrics
> HOST-RESOURCES-MIB::hrStorageAllocationUnits.1 = INTEGER: 4096 Bytes
> HOST-RESOURCES-MIB::hrStorageSize.1 = INTEGER: 391488
> HOST-RESOURCES-MIB::hrStorageUsed.1 = INTEGER: 391252
> =====
> 
> How I must process it to calculate actual memory usage for machine with
> 4GB RAM and without swap?
> 
> =====
> $ sysctl hw | egrep 'hw.(phys|user|real)'
> hw.physmem: 4243894272
> hw.usermem: 3580182528
> hw.realmem: 4294967296
> =====

Values returned by bsnmpd look weird to me as well, so I looked into it
a bit.  Excerpt from the snmp_hostres (as a standalone test case):
----
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>

#include <vm/vm_param.h>

#include <err.h>
#include <stdio.h>

static struct vmtotal mem_stats;

int
main(void)
{
        int mib[2] = { CTL_VM, VM_TOTAL };
        size_t len = sizeof(mem_stats);

        if (sysctl(mib, 2, &mem_stats, &len, NULL, 0) != 0)
                err(1, "sysctl");

        printf("real=%lu\n", mem_stats.t_rm);

        return (0);
}
----
output:
real=31632
----

Now the sysctl output:
----
$ sysctl vm.vmtotal
vm.vmtotal:
System wide totals computed every five seconds: (values in kilobytes)
===============================================
Processes:              (RUNQ: 1 Disk Wait: 0 Page Wait: 0 Sleep: 28)
Virtual Memory:         (Total: 547240K Active: 542480K)
Real Memory:            (Total: 126572K Active: 125600K)
Shared Virtual Memory:  (Total: 4612K Active: 0K)
Shared Real Memory:     (Total: 924K Active: 0K)
Free Memory:    3608396K
---
I can't map the output to anything on the system (16G RAM, 16G swap)
except for the "Free Memory", it matches.

31632 ("real") * 4096 ("pagesize") matches the "Real Memory" in sysctl
output.  Though to get anything resembling 16G, "real" needs to be
multiplied by 512 (K?).

As a wild guess, it seems that the units used are wrong here, or I
simply don't understand the meaning of these values.