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Date: Tue, 9 Jan 2007 06:15:44 -0800
From: Christopher Layne <clayne AT anodized DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: 1.7.0 CVS mmap failure
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On Tue, Jan 09, 2007 at 12:56:43PM +0100, Corinna Vinschen wrote:
> > Okay, I understand where you're coming from. Where I'm coming from is that it
> > is difficult to generate a test case that actually demonstrates the issue
> > outside of the scope of my application. Suffice to say, I do see the errors in
> > strace output - and I can see MapViewNT returning an error in the double-map
> > -so-we-can-have-4k-pseudopages version.
> 
> I'm under the impression you're getting something upside-down.  Windows
> has 4K system pages, but an allocation granularity of 64K.  For a long
> time I stubbornly tried to stick with 4K pagesize for POSIX applications,
> but the code got more and more complicated because there was always yet
> another situation which just didn't work correctly due to the 64K
> allocation granularity.

extern "C" size_t
getpagesize ()
{
  if (!system_info.dwPageSize)
    GetSystemInfo (&system_info);
  return (size_t) system_info.dwAllocationGranularity;
}

size_t
getsystempagesize ()
{
  if (!system_info.dwAllocationGranularity)
    GetSystemInfo (&system_info);
  return (size_t) system_info.dwPageSize;
}

Turns out I was reading these backwards, yes.

$ ./psz
psz == 4096, ag == 65536

I'll try and reanalyze some of the other stuff tomorrow.

-cl

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