Memory usage is wrong (usage vs cache)?

[tatref]

Hi,

It seems that the memory usage reported by the API memory_stats/usage is not correct if the container is doing a lot of IO and thus has lots of disk cache.

Example of a mysql database:

# docker stats
MEM USAGE / LIMIT     MEM %
329.6MiB / 2.868GiB   11.22%

The API shows:

check_docker.sh --containers prd-piwik-mysql --memory 500:1000:m
WARNING: prd-piwik-mysql memory is 784.765625m|prd-piwik-mysql_mem=784.765625m;500;1000;0;2936.6015625

This seems related to the issue moby/moby#10824

[tatref]

Further digging into the API, I found the following:

    "memory_stats": {
        "stats": {
            "cache": 477356032,
            "rss": 345579520,
        },
        "usage": 822935552
    },

I'm not sure how to fix this properly though.

What do you thing about taking just rss? or usage - cache?

[tatref]

I did the following change under check_memory:

    usage = inspection['memory_stats']['usage'] / UNIT_ADJUSTMENTS[units]
    cache = inspection['memory_stats']['stats']['cache'] / UNIT_ADJUSTMENTS[units]
    real_usage = usage - cache

Here is the check output:

OK: prd-piwik-mysql memory is 353.640625m|prd-piwik-mysql_mem=353.640625m;500;1000;0;2935.87890625

Compared with docker stats:

MEM USAGE / LIMIT     MEM %
353.6MiB / 2.867GiB   12.05%

[tatref]

Oups, I just realized you fixed this a while ago!

[timdaman]

Oh, sorry. I didn't realize that you were reporting the same issue. Glad it is working for you now.