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Date: Tue, 29 Jan 2008 14:59:25 -0800 (PST)
From: Travis Vitek <vitek@roguewave.com>
To: dev@stdcxx.apache.org
Subject: Re: [PATCH] STDCXX-705
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References: 
 <CFFDD219128FD94FB4F92B99F52D0A499A2B00@exchmail01.Blue.Roguewave.Com>
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Martin Sebor wrote:
> 
> Travis Vitek wrote:
>>  
>>>
>>> It looks like th original code was stepping 16MB (1024 * 1024 bytes)
>>> past bad_address. That should be well more than one page away. BTW, you
>>> can determine the kernel page size on most *nix platforms with sysconf
>>> (_SC_PAGESIZE).
>>>
>>> Travis
>>>
>> 
>> Of course the kernel memory page size from sysconf() isn't the same as
>> the virtual memory page size that you are talking about. :)
> 
> It's not? I thought both sysconf(_SC_PAGESIZE) and getpagesize()
> returned the size of the virtual page. I.e., whatever smallest
> unit mmap() allocates.
> 
> Martin
> 

I think I may have worded my response poorly. The page size, as returned by
sysconf(), is does not appear to be the same as the page size that is set by
chatr.

  $ cat u.cpp && aCC u.cpp
  #include <stdio.h>
  #include <unistd.h>

  int main ()
  {
      printf ("%ld\n", sysconf (_SC_PAGE_SIZE));
      return 0;
  }

  $ chatr +pd 1M +pi 1M a.out > /dev/null && ./a.out
  4096

  $ chatr +pd 4M +pi 4M a.out > /dev/null && ./a.out  
  4096

A quick glance at the documentation for chatr says that +pd and +pi are only
hints for the virtual memory page size, so that may explain the difference
I'm seeing. Interestingly, you can set values for up to 4GB.

Travis
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