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

Yuri wrote:
> 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.

Looking at sys/vmmeter.h, my assumptions above are wrong:

uint64_t        t_rm;           /* total real memory in use */

But that does not include the "wired" (and other) pages, so I'm not sure
about this metric usefulness.

In any case, you have the following:

HOST-RESOURCES-MIB::hrMemorySize.0 = INTEGER: 16734232 KBytes