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The pain to get real memory usage stats on physical SmartOS
Friday - Jan 10th 2014 - by - (2 comments)

For more than a year now I've been successfully monitoring SmartOS smartmachines with Nagios. To monitor the memory usage, I am using "check_mem" (https://github.com/Voxer/nagios-plugins/blob/master/check_mem) which works very well and allows me to create graphics (the perfdata code of this plugin was actually added by me).

Here an example of the graph:

Smartmachine memory usage

While this is working on smartmachines (the zones), the plugin does not work on physical servers.
To get the currently used memory value, the command kstat is used. If I launch the command on a physical (global zone) SmartOS, all zones are shown:

kstat -pc zone_memory_cap :::rss :::physcap
memory_cap:0:global:rss 0
memory_cap:1:57fc3d3a-5e64-4d04-bfb8-150521:rss 65212416
memory_cap:2:fd631bd1-bd33-41fa-9dcb-22b560:rss 320839680
memory_cap:3:e9490a97-1de4-4454-baa7-3f5c3e:rss 55779328
memory_cap:4:f6f05a1f-0f04-45a4-96dd-0006d0:rss 244248576
memory_cap:5:290fc8d8-6e6a-414b-967d-0a185d:rss 61616128
memory_cap:6:f2d169d8-20d2-41d4-8e43-8a9fc5:rss 2195832832

This would be OK - but the global zone's rss value is 0 (see above). So I started looking for alternatives, how to get the actual usage of the global zone.

One good alternative I found, was to use mdb:

echo ::memstat | mdb -k
Page Summary                Pages                MB  %Tot
------------     ----------------  ----------------  ----
Kernel                   11406904             44558   34%
ZFS File Data            12069177             47145   36%
Anon                      8802319             34384   26%
Exec and libs               12085                47    0%
Page cache                  25488                99    0%
Free (cachelist)            12979                50    0%
Free (freelist)           1220564              4767    4%

Total                    33549516            131052
Physical                 33549514            131052

There are some downsides of this command, though: The command takes nearly 4 seconds for the output (I can live with that) and I am not sure if the sum of the percentage correct. Sure, they sum up to 100% and I know that ZFS uses a lot of memory, but 36% of the whole system? But at least this is a working alternative.

Another way I found is to use prstat which in combination with -Z shows a summary of the zones. With -z a zone id can be used to retrieve the data for a specific zone:

prstat -z 0 -Z
    95 root        0K    0K sleep   99  -20  55:03:33 0.1% zpool-zones/182
 87597 root       22M   18M sleep   59    0   1:34:22 0.0% perl/1
 87596 root       24M   17M sleep   59    0   0:34:56 0.0% perl/1
  3622 root       32M   27M sleep   59    0   8:43:10 0.0% node/6
  3913 root       55M   35M sleep  100    -   5:38:20 0.0% node/5
  6022 root       17M   13M sleep   59    0   3:37:54 0.0% vmadmd/6
  3927 root     1936K 1344K sleep    1    0   0:00:00 0.0% ttymon/1
  4144 root     6688K 3144K sleep   29    0   0:00:00 0.0% inetd/3
  3824 root     1936K 1344K sleep    1    0   0:00:00 0.0% ttymon/1
    62 root     2572K 1448K sleep   29    0   0:00:04 0.0% pfexecd/3
  1531 root       12M 8200K sleep   29    0   0:19:40 0.0% nscd/31
  3920 root     1936K 1344K sleep    1    0   0:00:00 0.0% ttymon/1
    27 root     3100K 1636K sleep   29    0   0:00:16 0.0% dlmgmtd/14
    30 netadm   4500K 2748K sleep   29    0   0:00:07 0.0% ipmgmtd/3
   589 root     6640K 2812K sleep   29    0   0:00:00 0.0% syseventd/18
ZONEID    NPROC  SWAP   RSS MEMORY      TIME  CPU ZONE                       
     0       80  986M  651M   0.4%  86:36:28 0.1% global                     
Total: 80 processes, 557 lwps, load averages: 1.61, 1.68, 1.80

The interesting part comes after the process list. The column RSS is the amount of memory used by the global zone. 

As prstat is an interactive command (like top on Linux), you have to play around with it a little to be able to save the output into a file:

prstat -z 0 -Z 1 1 > output.txt

I have now different options to patch the "check_mem" plugin for SmartOS:

  • Use the same kstat command as already used in the plugin but add the rss values of each found zone to a total rss size. Issue here: The global zone itself uses memory, too. This value is missing in kstat.
  • Use mdb output and use the third column (MB) to calculate the current usage. The good part here is that I don't need another command to get the total physical memory value. I just have to watch out that I don't count "ZFS File Data" as used memory but rather as cached memory.
  • Use the prstat output, but without declaring the global zone (-z 0) so I get the current RSS value for all active zones (including the global zone). Basically the same logic as using kstat but prstat contains the rss value for the global zone. 

When doing a calculation of the different methods, the results vary:

kstat mem rss (sum): 34189 MB = 33.39 GB
memstat/mdb kernel: 44898 MB = 43.85 GB
prstat rss (sum): 34659 MB = 33.85 GB
Joyent sdc used RAM: 37376 MB = 36.5 GB

So the closest result to the one from SDC is the sum of all prstat rss values. If I subtract the global zone's rss value I get the same rss value as from kstat. So that seems correct.

Whatever method I will decide for, the result will be pushed upsteam into the Voxer Nagios-Plugins repository (https://github.com/Voxer/nagios-plugins).


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Comments (newest first):

ck from Switzerland wrote on Feb 24th, 2016:
Hi UX-Admin. Maybe in your point of view. But if you sell zones to your customers (and that's the case in that setup), you need to know their memory usage in order to generate correct invoices.
EDIT: Oh, I misunderstood your comment. Yes, on the global zone it might be wrong, however we needed at least some graph in our monitoring to understand the memory consumption on a physical level. We never got to the point where this is 100% accurate, but it gave us an idea.
Luckily we ditched SmartOS after a while (it was too much of a headache with customer requests).

UX-admin wrote on Feb 24th, 2016:
The global zone keeps track of the entire system's memory usage, and all zones share that same memory. Therefore, keeping track of each individual zone's aggregate memory usage is pointless, not to mention incorrect. If you however have zones whose processes are leaking memory, then the indivdual process which is leaking memory should be tracked down and debugged. What you are attempting to do is really unnecessary.

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