Nginx Caching strategy

[cachenewbie]

All -  Is there a high level tutorial on how nginx does caching ?  Does
it use mmap to map the cache directory/file into memory and share it
with all nginx worker processes (and use sendfile to send it out to the
socket) ?  Or does it use directIO to open the file and use regular
read/write syscalls ? This is for Linux debian platform.

Thanks,

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,137051,137051#msg-137051