[erlang-questions] Erlang garbage collection

[Dmitry Kolesnikov]

Hello,

One of the docker problem is that resources are constrained via cgroups. The ordinary system calls and  utilities reports host memory. Thus, your dockerized Erlang nodes assumes 64Gb RAM availability and they will adjust gc accordingly. 

I do not see any better solution then set hard memory limit either to docker container or Erlang node.
Unfortunately, none of these options are available for you. I am afraid that you need to tune Erlang memory allocators to achieve desired effect. Here is some references:

https://erlangcentral.org/euc-2014-lukas-larsson-memory-allocators-in-the-vm-memory-management-battle-stories/#.VE39WYc3bQc

http://erlang.org/doc/man/erts_alloc.html

BTW, I am going to hit same issue during next week(s) due to my Erlang to Docker roll-out project. I’d be glad to collaborate on it to find best solution. 

Best Regards, 
Dmitry  


> On 25 Oct 2014, at 21:37, Viacheslav V. Kovalev <kovyl2404@REDACTED> wrote:
> 
> Hi all!
> I need your help in investigation of issue with erlang memory consumption. How typical, isn't it?
> 
> We have two different deployment schemes.
> * In first scheme we running many identical nodes on small virtual machines (in Amazon AWS),
> one node per machine. Each machine has 4Gb of RAM.
> * In another deployment scheme we running this nodes on big baremetal machines (with 64 Gb of ram),
> with many nodes per machine. In this deployment nodes are isolated in docker containers
> (with memory limit set to 4 Gb).
> 
> I've noticed, that heap of processes in dockerized nodes are hogging up to 3 times much more RAM, than
> heaps in non-dockerized nodes with identical load. I suspect that garbage collection in non-dockerized nodes is more aggressive.
> Unfortunately, I don't have any garbage collection statistics, but I wanna obtain it ASAP.
> 
> To give more information, I should say that we are using HiPE R17.1 on ubuntu 14.04 with stock kernel. In both schemes we are
> running 8 schedulers per node, and using default `fullsweep_after` flag.
> 
> My blind suggestion is that erlang default garbage collection relies (somehow) on /proc/meminfo (which is not actual in dockerized environment).
> I am not C-guy and not familar with emulator internals, so could someone point me to places in erlang sources that are responsible for garbage collection
> and some emulator options which I can use to tweak this behavior?
> 
> Viacheslav V. Kovalev
> Software engineer, Tradingview.
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