>I am assuming that the initial private mmap fails
>to page in the actual underlying data. The anonymous mapping version
>reads the data, filling in pages in memory while doing that. When the
>file is closed the inode and pages linger around and the second private
>mmap finds these pages already there and doesn't need to trigger paging
>things in form disk anymore.

Ok, so you are talking about a buffer cache having the data.  That is
possible.   I don't know if this related to the rdsinit rvm problem I
was having when I was trying to get rdsinit to use private mapping.

-- 
Phil Nelson                    NetBSD: http://www.netbsd.org
e-mail: phil@cs.wwu.edu        Coda: http://www.coda.cs.cmu.edu
http://www.cs.wwu.edu/~phil