How to set keys_zone for proxy_cache_path on linux


I was wondering how to set the keys_zone parameter of the

The wiki says
"Zone size should be set proportional to number of pages to cache. The
size of the metadata for one page (file) depends on the OS; currently it
is 64 bytes for FreeBSD/i386, and 128 bytes for FreeBSD/amd64. "

Are these numbers also true for linux? If not, what are they?