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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