Erlang memory fragmentation

Question

Our Erlang server looks have a serious memory leak, the VM memory usage is low but top is high.

Env

Erlang: R16B02 OS: Ubuntu 12.04.5 LTS \\n \\l X86_64

Erlang VM

> erlang:memory().
[{total,424544992},
 {processes,293961840},
 {processes_used,293937232},
 {system,130583152},
 {atom,553569},
 {atom_used,521929},
 {binary,9794704},
 {code,14041920},
 {ets,5632280}]

Allocated Memory

> recon_alloc:memory(allocated).
2570059776

 recon_alloc:memory(allocated_types).
[{binary_alloc,163577856},
 {driver_alloc,11010048},
 {eheap_alloc,2165309440},
 {ets_alloc,11010048},
 {fix_alloc,50855936},
 {ll_alloc,156237824},
 {sl_alloc,2097152},
 {std_alloc,6815744},
 {temp_alloc,3145728}]

allocate binary

> recon:bin_leak(5).
[{<0.440.0>,-769,
  [{current_function,{gen_server,loop,6}},
   {initial_call,{proc_lib,init_p,5}}]},
 {<0.446.0>,-230,
  [{current_function,{gen_server,loop,6}},
   {initial_call,{proc_lib,init_p,5}}]},
 {<0.450.0>,-179,
  [{current_function,{gen_server,loop,6}},
   {initial_call,{proc_lib,init_p,5}}]},
 {<0.12497.0>,-147,
  [{current_function,{gen,do_call,4}},
   {initial_call,{proc_lib,init_p,5}}]},
 {<0.434.0>,-145,
  [{current_function,{cberl_worker,mget,4}},
   {initial_call,{proc_lib,init_p,5}}]}]

Do garbage

7> erlang:garbage_collect().
true
8> erlang:memory().
[{total,381782256},
 {processes,251371752},
 {processes_used,251361352},
 {system,130410504},
 {atom,553569},
 {atom_used,521929},
 {binary,9230384},
 {code,14041920},
 {ets,5675528}]
> recon_alloc:memory(allocated_types).
[{binary_alloc,150994944},
 {driver_alloc,11010048},
 {eheap_alloc,2154823680},
 {ets_alloc,11010048},
 {fix_alloc,50855936},
 {ll_alloc,156237824},
 {sl_alloc,2097152},
 {std_alloc,6815744},
 {temp_alloc,3145728}]

Fragmentation

And I check recon_alloc:fragmentation(current) and recon_alloc:fragmentation(max) , find some allocator current usage is lower than max usage.

Current usage

 {{binary_alloc,0},
  [{sbcs_usage,1.0},
   {mbcs_usage,0.037804497612847224},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,178384},
   {mbcs_carriers_size,4718592}]},
 {{binary_alloc,2},
  [{sbcs_usage,2.0},
   {mbcs_usage,0.05326200786389803},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,4775112},
   {mbcs_carriers_size,89653248}]},
 {{binary_alloc,1},
  [{sbcs_usage,2.0},
   {mbcs_usage,0.0643930146188447},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,4456384},
   {mbcs_carriers_size,69206016}]},

Max usage

 {{binary_alloc,0},
  [{sbcs_usage,1.0},
   {mbcs_usage,0.7732696533203125},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,24324960},
   {mbcs_carriers_size,31457280}]},
 {{binary_alloc,2},
  [{sbcs_usage,1.0},
   {mbcs_usage,0.938345729714573},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,149064912},
   {mbcs_carriers_size,158859264}]},
 {{binary_alloc,0},
  [{sbcs_usage,1.0},
   {mbcs_usage,0.7732696533203125},
   {sbcs_block_size,0},
   {sbcs_carriers_size,0},
   {mbcs_block_size,24324960},
   {mbcs_carriers_size,31457280}]},

Does is mean Erlang server have lots of Memory fragmentation and How can I move on?

Answer 1

The memory fragmentation in Erlang is much more complicated than it looks like, and is a deep problem already approached.

Take a look at this post from Fred https://blog.heroku.com/logplex-down-the-rabbit-hole#how-erlang-39-s-memory-stuff-works

It shows the whole problem, the Erlang memory fragmentation is not solved but can be reduced.