真正看懂TOP的进程内存（VIRT、RES、SHR）

- 64位系统内核占据128T地址范围：0xFFFF FFFF FFFF FFFF – 0x0000 7FFF FFFF FFFF
- 64位系统进程占据128T地址范围：0x0000 7FFF FFFF FFFF – 0x0000 0000 0000 0000（从高到低：栈、映射、堆、BSS、数据、代码、保留）TOP的RES即实际用页表映射到物理内存的大小，使用多少映射多少，按需满足。从实验来看最小映射单位为4KB（用1个字节也映射4KB）。

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>

// gcc -g malloc.c -o malloc

void fun_sig(int sig) {
  printf("recv sig %d, exit...\n",sig);
  exit(0);
}

int main() {
  int i;
  size_t s;
  char *ptr;

  signal(SIGINT, fun_sig);

  s = 100 * 1024 * 1024;
  ptr = malloc(s);
  for (i = 0; i < 100 * 1024 * 1024; i++) {
    //if (i % (1024*1024) == 0)
    *(ptr + i) = 0xFF;
  }
  printf("malloc done.\n");
  while(1);
  return 0;
}

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>


// gcc -g -lpthread ph.c -o ph

void* worker(void* arg) {
  // printf("c");
  // char *xx = malloc(1000);
  // *(xx) = 0x12;
  // *(xx + 51) = 0x12;
  // free(xx);
  return NULL;
}

void fun_sig(int sig) {
  printf("recv sig %d, exit...\n",sig);
  exit(0);
}

int main() {

  int i;

  signal(SIGINT, fun_sig);

  for (i = 0; i < 100000; i++) {
    pthread_t t;
    int ret;
    ret = pthread_create(&t, NULL, worker, NULL);
    if (ret != 0) {
      printf("pthread_create error, ret=%d, i=%d.\n",ret, i);
      while(i);
    }
    // pthread_join(t, NULL);
  }

  printf("all thread created.\n");
  while(i);

  return 0;
}

pthread_create error, ret=11, i=32745.

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
26706 mingjie   20   0  256.0g 274.6m   0.6m R 100.0  0.9   0:16.87 ./ph

$ pmap -x 22359
00007f3cf591c000    8192       8       8 rw---   [ anon ]
00007f3cf611c000       4       0       0 -----   [ anon ]
00007f3cf611d000    8192       8       8 rw---   [ anon ]
00007f3cf691d000       4       0       0 -----   [ anon ]
00007f3cf691e000    8192       8       8 rw---   [ anon ]
00007f3cf711e000       4       0       0 -----   [ anon ]
...
...
$ pmap -x 22359 | grep 8192 | wc -l
32746

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	char *addr;
	size_t s = 100 * 1024 * 1024;

	addr = mmap(NULL, s, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	// *addr = 1;

	switch (fork())
	{
	case -1:
		fprintf(stderr, "fork() failed\n");
		exit(EXIT_FAILURE);

	case 0:
		printf("Child started, value = %d\n", *addr);
		for (int i = 0; i < s; i++)
		{
			*(addr + i) = 0xFE;
		}

		printf("Child started, value = %d\n", *addr);
		while(1);
		exit(EXIT_SUCCESS);

	default:
		while(*(addr + s/2) != -2);
		int kk;
		for (int i = 0; i < s / 2; i++)
		{
			kk = *(addr + i);
		}
		while(kk);
		if (wait(NULL) == -1)
		{
			fprintf(stderr, "wait() failed\n");
			exit(EXIT_FAILURE);
		}

		printf("In parent, value = %d\n", *addr);
		if (munmap(addr, sizeof(int)) == -1)
		{
			fprintf(stderr, "munmap()() failed\n");
			exit(EXIT_FAILURE);
		}
		exit(EXIT_SUCCESS);
	}
}

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f9a61f8e000  102400       0       0 rw-s- zero (deleted)

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f9a61f8e000  102400       4       0 rw-s- zero (deleted)

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f12d530c000  102400       0       0 rw-s- zero (deleted)

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f12d530c000  102400  102400  102400 rw-s- zero (deleted)

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f236a1db000  102400   51204   51200 rw-s- zero (deleted)

Address           Kbytes     RSS   Dirty Mode  Mapping
00007f236a1db000  102400  102400  102400 rw-s- zero (deleted)