Broken autoconf mmap test

[Brian Ford]

On Thu, 24 Mar 2011, Corinna Vinschen wrote:

> In case of MAP_PRIVATE, anonymous maps are implemented using
> VirtualAlloc.  The size of the allocated space is always a multiple of
> 64K.  After creating it, the file content is simply copied over.
> Full stop.  Easy.

I'd hate to pay the full read/write file I/O penalty on map/unmap for
applications that use this technique to do small amounts of random I/O
(normally just the touched pages).  You would need page initialized/dirty
bit book keeping combined with paged I/O I think to do it well for both
read and write.

-- 
Brian Ford
Staff Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained crew...