test mmap rss

Main.java

public class Main {
	public static void main(String[] args) {
		var arr = new byte[(1024 * 1024)][];
		new Thread(() -> {
			while (true) {
				var total = Runtime.getRuntime().totalMemory();
				System.out.println(total);
				try {
					Thread.sleep(5 * 1000);
				} catch (Exception ignore) {
				}
			}
		}).start();
		while (true) {
			for (int i = 0; i < 1024 * 1024; ++i) {
				arr[i] = new byte[400];
			}
			for (int i = 0; i < 1024 * 1024; ++i) {
				arr[i] = null;
			}
		}
	}
}

run-java.sh

#!/bin/bash

set -e

javac Main.java
java -XX:+UseZGC -Xmx2G -verbose:gc Main

test-mmap-rss.c

#define _GNU_SOURCE

#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <linux/memfd.h>
#include <fcntl.h>
#include <string.h>
#include <inttypes.h>

int main() {
	int fd = memfd_create("mytest", MFD_CLOEXEC);
	printf("fd = %d\n", fd);
	int err = ftruncate(fd, 1073741824);
	if (err) {
		perror("ftruncate failed");
		return 1;
	}
	err = fallocate(fd, 0, 0, 0x33400000);
	if (err) {
		perror("fallocate failed");
		return 1;
	}
	void* mmap_res_1 = mmap((void*)0x100000000, 0x33400000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, fd, 0);
	if (mmap_res_1 == NULL) {
		perror("mmap 1 failed");
		return 1;
	}
	printf("mmap_res_1 = %lu\n", (size_t) mmap_res_1);
	memset(mmap_res_1, 1, 0x33400000);
	for (int i = 0; i < 64; ++i) {
		printf("iteration = %d\n", i);
		uint64_t loc = (2L + i) << (4 * 8);
		void* mmap_res_2 = mmap((void*)loc, 0x33400000, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, fd, 0);
		if (mmap_res_2 == NULL) {
			perror("mmap 2 failed");
			return 1;
		}
		printf("mmap_res_2 = %lu\n", (size_t) mmap_res_2);
		printf("mmap_res_2[last] = %d\n", ((char*)mmap_res_2)[ 0x33400000 - 1 ]);
		for (uint64_t j = 0; j < 0x33400000; ++j) {
			char v = ((char*)mmap_res_2)[j];
			if (v != (i + 1)) {
				printf("invalid value at %lu = %d, expecting %d\n", j, v, (i + 1));
				break;
			}
		}
		memset(mmap_res_2, i + 2, 0x33400000);
	}
	sleep(120);
	return 0;
}