memory used by Erlang VM

[Vyacheslav Levytskyy]

It's linux (ubuntu). I read /proc/[pid]/statm, take RSS number of pages 
(the 2nd value in the line of that file) and calculate memory used by 
Erlang VM as RSS x page size (read as "getconf PAGESIZE").

On 31.01.2020 19:59, Jesper Louis Andersen wrote:
> When you say /proc/pid, what are you looking at specifically in there? 
> It is a bit different depending on which Unix you run on, so a simple 
> example will help a lot.
>
> In particular, my early guess is going to be virtual memory vs 
> physical RSS mapping. The former can be much higher than the latter. 
> Especially in system such as Linux, which allow overcommitting memory.
>
> On Fri, Jan 31, 2020 at 7:22 PM Vyacheslav Levytskyy 
> <v.levytskyy@REDACTED <mailto:v.levytskyy@REDACTED>> wrote:
>
>     Hello,
>
>     I wonder why memory used by Erlang VM as reported by the kernel
>     via the
>     /proc/pid differs from erlang:memory(total). In my current
>     configuration
>     I observe realistic response from erlang:memory(total) and much lower
>     values from the /proc/pid.
>
>     I'm not surprised by the difference itself, but rather by the fact
>     that
>     the /proc/pid gives unrealistically lower values -- I'm not 100%
>     sure,
>     but it looks like RabbitMQ is using the /proc/pid approach by
>     default,
>     proposing also recon_alloc:memory(allocated) and
>     erlang:memory(total) as
>     available options of Erlang VM memory consumption calculation
>     strategy.
>
>     Does anybody have insights of what and why is going on with those
>     calculations of memory used by Erlang VM? Is it possible to select
>     one
>     strategy beforehand for my Erlang app, or I must measure on each new
>     configuration what looks more precise? Should I compare and change
>     the
>     strategy during run-time, or after I selected a strategy once for my
>     configuration I can be sure that selected approach always better than
>     other two?
>
>     Thank you,
>     Vyacheslav
>
>
>
> -- 
> J.
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