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Re: Broken autoconf mmap test
- From: Brian Ford <Brian dot Ford at FlightSafety dot com>
- To: cygwin-developers at cygwin dot com
- Date: Thu, 24 Mar 2011 09:31:28 -0500
- Subject: Re: Broken autoconf mmap test
- References: <4D891A55.6050601@cornell.edu> <20110323091921.GB10657@calimero.vinschen.de> <4D89D4AA.6070903@cornell.edu> <20110323132622.GM31220@calimero.vinschen.de> <4D89FEC7.3000107@cornell.edu> <20110323154421.GN31220@calimero.vinschen.de> <4D8A308F.508@cornell.edu> <4D8A3206.7070502@redhat.com> <4D8A3329.7050009@redhat.com> <20110323181507.GV31220@calimero.vinschen.de> <20110324095945.GD31220@calimero.vinschen.de>
- Reply-to: cygwin-developers at cygwin dot com
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...