evict not work with gcc -O0

[pukaifei]

1. If vmtouch.c is compiled with gcc -O2, evict succeeds by calling posix_fadvise.
   But with gcc -O0, evict fails and mincore shows that memory is still used.
   What's the difference between -O2 and -O0 for posix_fadvise ?

2. If use mmap, mlock, munlock sequentially, then call posix_fadvise and mincore shows that memory is still used.
   If mlock and munlock is skipped, posix_fadvise succeeds.
   I know that posix_fadivse is async, but how does lock affects it ?

Thanks !