memory-mapped files

[Brad Roberts]

bearophile wrote:
 >> What the heck is going on? When does memory mapping actually help?<
> 
> You are scanning the file linearly, and the memory window you use is
> probably very small. In such situation a memory mapping is probably
> not the best thing. A memory mapping is useful when you for example
> operate with random access on a wider sliding window on the file.

You can drop the 'sliding' part.  mmap tends to help when doing random
access (or sequential but non-contiguous maybe) over a file.  Pure
streaming is handled pretty well by both patterns.  One nicity with mmap
is that you can hint to the os how you'll be using it via madvise.  You
can't do that with [f]read.

Later,
Brad