user/sysinfotest.c : is there a bug?

[qin-you]

int
countfree()
{
uint64 sz0 = (uint64)sbrk(0);
struct sysinfo info;
int n = 0;

while(1){
if((uint64)sbrk(PGSIZE) == 0xffffffffffffffff){ /* loop forever if there is no more mem originally?/
break;
}
n += PGSIZE; / undercount one if there is only one page left originally ?*/
}
}

[ljluestc]

#include <unistd.h>
#include <sys/sysinfo.h>

int countfree() {
uint64_t sz0 = (uint64_t)sbrk(0);
struct sysinfo info;
int n = 0;

while (1) {
    if ((uint64_t)sbrk(PGSIZE) == (uint64_t)-1) { /* Check if sbrk returns -1 when there's no more memory */
        break;
    }
    n += PGSIZE;
}

return n;

}