devmem2 is not writing to the address specified - c

Question

I am trying to change a variable's content of a program with devmem2. Simply:
static inline __attribute__ ((always_inline))
void clflush(volatile void *p)
{
asm volatile ("clflush (%0)\n"::"r" (p):"memory");
}
uint64_t get_pfn(uint64_t entry) {
return ((entry) & 0x3fffffffffffff);
}
uint64_t get_phys_addr(uint64_t v_addr)
{
uint64_t entry;
uint64_t offset = (v_addr/4096) * sizeof(entry);
uint64_t pfn;
int fd = open("/proc/self/pagemap", O_RDONLY);
assert(fd >= 0);
int bytes_read = pread(fd, &entry, sizeof(entry), offset);
close(fd);
assert(bytes_read == 8);
assert(entry & (1ULL << 63));
pfn = get_pfn(entry);
assert(pfn != 0);
return (pfn*4096) | (v_addr & 4095);
}
int main(){
int a = 44;
uint64_t v_addr = (uint64_t) &a;
printf("%lx\n",v_addr);
uint64_t p_addr = get_phys_addr(v_addr);
printf("%lx\n",p_addr);
clflush(&a);
sleep(20);
int b = a;
printf("value of b: %d\n",b);
printf("value of b: %d\n",a);
uint64_t v_addr2 = (uint64_t) &b;
printf("%lx\n",v_addr2);
uint64_t p_addr2 = get_phys_addr(v_addr2);
printf("%lx\n",p_addr2);
}
I am trying to change the content of variable "a" while sleeping with devmem2. Consider that my program prints "17580fab8" as the physical address of "a". I am executing devmem2 in another tab like this:
sudo devmem2 -x17580fab8 w 0x1235
So, after sleeping 20 seconds, I would expect the value of a and b to 0x1235. However, they do not change. The output when I run devmem2 while my program sleeps is this:
/dev/mem opened.
Memory mapped at address 0x7f464d50c000.
Value at address 0x0 (0x7f464d50c000): 0x1235
Written 0x1235; readback 0x1235
devmem2 claims to "read/write from/to any location in memory". Is it wrong? Because how can it write to my program's pages?