madvise_example.c

#include <ctype.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/mman.h>
#include <signal.h>

typedef void(*Callback)(uintptr_t /*start*/, unsigned long/*size*/, const char* /*prot flags*/, const char* /*fname*/, unsigned long /*pss*/);

void ForEachMapEntry(Callback callback) {
  FILE* f = fopen("/proc/self/smaps", "r");
  unsigned long start = 0, end = 0;
  char mapped_file[512] = {};
  char prot[5] = {};
  while(!feof(f)) {
    char line[512];
    fgets(line, sizeof(line), f);
    if (isxdigit(line[0])) {
      sscanf(line, "%lx-%lx %s %*s %*s %*s %[^\n]\n", &start, &end, prot, mapped_file);
    } else if(strncmp(line, "Pss:", 4) == 0) {
      int pss = 0;
      sscanf(line, "Pss: %d kB", &pss);
      callback(start, end-start, prot, mapped_file, pss);
    }
  }
  fclose(f);
}

unsigned long g_total_pss;
void CalcTotalPSS(uintptr_t start, unsigned long size, const char* prot, const char* mapped_file, unsigned long pss) {
  //printf("%s %s %lu\n", prot, mapped_file, pss);
  g_total_pss += pss;
}
void PrintSelfPSS() {
  g_total_pss = 0;
  ForEachMapEntry(CalcTotalPSS);
  printf("Total PSS: %lu kB\n", g_total_pss);
}

void DropRXPages(uintptr_t start, unsigned long size, const char* prot, const char* mapped_file, unsigned long pss) {
  if (strncmp(prot, "r-x", 3) == 0)
    madvise((void*)start, size, MADV_DONTNEED);
}

void FaultRXPages(uintptr_t start, unsigned long size, const char* prot, const char* mapped_file, unsigned long pss) {
  volatile int total = 0;
  if (strncmp(prot, "r-x", 3) == 0) {
    unsigned long s;
    for (s = 0; s < size; s += sizeof(int))
      total += *((int*)(start + s));
  }
}

void sighandler(int _) {
  printf("Madvising all R-X pages\n");
  ForEachMapEntry(DropRXPages); // Drop all r-x pages.
  PrintSelfPSS();
}

int main(int argcv, char** argv) {
  // Page faulting on all r-x mapped files to gather some PSS.
  ForEachMapEntry(FaultRXPages);
  PrintSelfPSS();
  signal(SIGUSR2, sighandler);
  for(;;) sleep(60);
  return 0;
}