Can you detect memory allocated via malloc in C (via Ruby's FFI) when calling GC.stat?

README.md

Results of running this:

❯ ruby ffi.rb
Allocating 1048576 via malloc in FFI
	before malloc: 		maxrss: 	37044224
	before scribble: 	maxrss: 	37093376
	after scribble: 	maxrss: 	38141952
heap_live_slots: 48069 -> 48073 (diff: 4)
heap_free_slots: 4098 -> 4094 (diff: -4)
total_allocated_objects: 151713 -> 151717 (diff: 4)
malloc_increase_bytes: 659264 -> 660640 (diff: 1376)
oldmalloc_increase_bytes: 659264 -> 660640 (diff: 1376)


Allocating 1073741824 via malloc in FFI
	before malloc: 		maxrss: 	38141952
	before scribble: 	maxrss: 	38141952
	after scribble: 	maxrss: 	1111883776
heap_live_slots: 48103 -> 48104 (diff: 1)
heap_free_slots: 4064 -> 4063 (diff: -1)
total_allocated_objects: 151747 -> 151748 (diff: 1)
malloc_increase_bytes: 661840 -> 662736 (diff: 896)
oldmalloc_increase_bytes: 661840 -> 662736 (diff: 896)

ffi.rb

require 'ffi'

module MyLib
  extend FFI::Library
  ffi_lib './my_ffi.o'
  attach_function :consume_many_memories, [:int], :void
end

def report_mem(size)
  puts "Allocating #{size} via malloc in FFI"
  before = GC.stat
  MyLib.consume_many_memories(size)
  after = GC.stat

  before.each_key do |key|
    before_val = before.fetch(key)
    after_val = after.fetch(key)
    if after_val != before_val
      puts "#{key}: #{before_val} -> #{after_val} (diff: #{after_val - before_val})"
    end
  end
end

report_mem(1024*1024)
puts
puts
report_mem(1024*1024*1024)

my_ffi.c

// Build with: cc -dynamiclib -o my_ffi.o my_ffi.c
#include "my_ffi.h"

static uint8_t *mem;

void report_mem_usage() {
  struct rusage r_usage;
  getrusage(RUSAGE_SELF, &r_usage);
  printf("\tmaxrss: \t %ld", r_usage.ru_maxrss);
}

void consume_many_memories(uint32_t size) {
  printf("\tbefore malloc: \t");
  report_mem_usage();
  printf("\n");
  mem = (uint8_t*)(malloc(size));
  // scribble into the allocated memory to force a 'real' allocation
  printf("\tbefore scribble: ");
  report_mem_usage();
  printf("\n");
  for (uint32_t i = 0; i < size; i++) {
    *mem = 1;
    mem++;
  }
  printf("\tafter scribble: ");
  report_mem_usage();
  printf("\n");
}

my_ffi.h

#ifndef _MYLIB_H_
#define _MYLIB_H_

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/resource.h>

extern void consume_many_memories(uint32_t);

#endif