[ccache] [patch] Massive performance degradation with direct mode due to bypassing filesystem cache with mmap (Mac/PPC)

[tridge at samba.org]

Hi Joel,

The other disadvantage of using mmap() is error handling. If you are
doing a build while a include file is changing size (eg. someone is
editing) then with mmap() you will either get a bus error signal or
you'll see zero filled pages, which is very hard to handle gracefully
(it is possible, its just very messy!).

If you use read() you get saner error handling. That's the main reason
I switched rsync away from using mmap() quite a while ago.

Cheers, Tridge