Explain box.runtime.info()

[DifferentialOrange]

There are a few lines about box.runtime metrics in doc:

box.runtime.info():

lua is the heap size of the Lua garbage collector;
used is the current memory size used by Lua.

Metrics runtime:

tnt_runtime_lua Lua garbage collector size in bytes
tnt_runtime_used Number of bytes used for the Lua runtime

tnt_runtime_lua seems to be the same as (or something close to) box.info.memory().lua:

At the same time, tnt_runtime_used seems monotonic and always greater than tnt_runtime_lua

It's hard to notice any similarities between slab and runtime arena:

So the question is: what is box.info.memory().used (tnt_runtime_used) and how we should monitor it? Is tnt_runtime_used reaching 2 Gb Lua memory limit is an alert condition or not?

[Totktonada]

See also tarantool/doc#2911.

[DifferentialOrange]

The exact answer I came up with based on tarantool/doc#2911 is

tnt_runtime_used is memory used by runtime arena. Runtime arena stores network buffers, tuples created with box.tuple.new and other objects allocated by application not covered by basic Lua mechanisms (spaces data and indexes are not included here, see memtx/vinyl arena).