Question

DigitalOcean is calculating wrong the memory graph in monitoring?

Hello, I’m trying to fully understand the way DigitalOcean is calculating memory usage.

From the docs: DigitalOcean calculates memory consumption by evaluating memory information exposed in /proc/meminfo. On DigitalOcean, used memory is calculated by subtracting free memory and memory used for caching from the total memory amount.

If I expose the numbers on my droplet:

MemTotal:        3880364 kB
MemFree:          259960 kB
MemAvailable:    2647216 kB
Buffers:               0 kB
Cached:          1432548 kB
....
Slab:            1457128 kB
SReclaimable:    1371832 kB
....

The results are 3880364 MemTotal - (259960 MemFree + 1432548 Cached) = 2187856 kB This is about 56% (the same number that is indicated on monitoring graph)

On the other side, if I compare this output with the free command:

              total        used        free      shared  buff/cache   available
Mem:        3880364      847548      297784      129948     2735032     2615692
Swap:             0           0           0

I see that the used memory is 847548 kB, so this would be around 21%. You can also figure out that the value for buff/cache in free command is different from the /proc/meminfo command Cached value.

I think that DigitalOcean needs to also add the SReclaimable value from /proc/meminfo to the sum on the cache field.

SReclaimable: The part of the Slab that might be reclaimed (such as caches)

If we sum SReclaimable and Cached values we get: 2804380 kB. That’s pretty close to the buff/cache value on the free command.

After looking at some comparison charts on the Red Hat website Interpreting /proc/meminfo and free output for Red Hat Enterprise Linux 5, 6 and 7 I have found the match from the free and /proc/meminfo field:

free output coresponding /proc/meminfo fields
Mem: buff/cache Buffers + Cached + Slab

In summary, do you think that DigitalOcean needs to add the SReclaimable value? And show memory usage as subtracting free memory and memory used for caching (Cached & SReclaimable) from the total memory amount?

Maybe I’m far away wrong, I’m no linux expert… What do you think?


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Hi Daniel,

This is an interesting question!

I think that this is already the case. For example, here’s my current memory usage according to the graphs:

Memory graph - 61%

It is currently at around 61.41%. It is a small Droplet and the total available RAM is 1006756KB.

So If we do 1006756KB - 61.42%, we would get about 388406KB available RAM. And then if I run the free command I get 382476 which is pretty close to the 388406KB value:

                 total        used        free      shared  buff/cache   available
Mem:        1006756      423508       80004        9936      503244      382476

Memory Current Usage

What is the current version of your do-agent? I could suggest upgrading it to the latest version, maybe there are some improvements in how the available RAM is calculated.

Also the do-agent is open source, if you are interested you could take a look at the source code here:

https://github.com/digitalocean/do-agent

If you believe that there is still something wrong with the calculation, I would suggest creating an issue in GitHub.

Regards, Bobby

Hey there @danielpcharrua! Our Engineering team has deployed changes to accommodate this and memory graphs now show (MemTotal - MemAvailable) / MemTotal. This formula is also used for memory utilization alerts. This does require your Droplet has the up-to-date agent installed (version 3.10.1+) and that your Droplet has a Linux kernel with version 3.14+

Folks, if you agree with this please upvote the idea here:

https://ideas.digitalocean.com/ideas/CPX-I-17