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Why would the free command be reporting a much different mem usage number vs cgroup?

$ free -b total used free shared buff/cache available Mem: 2096914432 520863744 1112170496 35389440 463880192 1356828672 Swap: 2145382400 0 2145382400 $ cat /sys/fs/cgroup/memory/memory.usage_in_bytes 857239552

The documentation for cgroups says that memory.usage_in_bytes is a "fuzz value". I'm guessing that just means it reports an estimate that's close to the actual value. Even if it's an estimate, I don't think it should be this far off.

I'm running Linux Mint 18.2 in a VirutalBox VM.

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memory.usage_in_bytes and memory.max_usage_in_bytes report RSS+CACHE, so in terms of your free output:

memory.usage_in_bytes ~= free.used + free.(buff/cache) - (buff)

You may also be interested in /sys/fs/cgroup/memory/memory.stat, though I still couldn't find/compute the free.used value from the /sys/fs/cgroup/memory/memory.stat output.

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    What's the difference between free.(buff/cache) and (buff) in this answer? It's not clear where you're getting the (buff) value from. free.used and free.(buff/cache) are clearly from the output of running free. Commented Jul 14, 2021 at 2:06
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    @davidparks21 as far as I recall, the thing is that you cannot find pure (buff), but memory.usage_in_bytes seems to only include the cache Commented Jul 14, 2021 at 6:45

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