Date: Tue, 25 Jan 2022 07:55:36 +0300 From: Yuri <yuri@aetern.org> To: freebsd-questions@freebsd.org Subject: Re: snmp oid for memory usage, vmstat -i and others Message-ID: <0c8e1634-d4e2-2ecb-0af4-9f4eceab9124@aetern.org> In-Reply-To: <bd565507-019d-6fe9-6589-49413e5e1bb6@otcnet.ru>
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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.
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