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From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: Is the Ada run-time required to detect out-of-memory conditions?
Date: Sun, 23 May 2004 10:20:24 +0200
Organization: AdaCL
Message-ID: <3786783.CRZ4Sa361O@linux1.krischik.com>
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Date: 2004-05-23T10:20:24+02:00
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Robert I. Eachus wrote:

> Martin Krischik wrote:
> 
>> Just a thought: The page size on Intel CPU's is 4 kb. So most OS's on
>> Intel CPU will only handle mguarantyequests of at least one page.
>> 
>> I find it interesting that with request significantly larger then one
>> page everything seems Ok.
>> 
>> Lets Think: With GNAT allocation from the standart storrage pool are just
>> passed down to C's malloc ().
>> 
>> When smaller memory is requested most C compiler will bundele several
>> requests into one page request.
>> 
>> When larger  memory is requested some C compiler will just pass the
>> request on to the OS and some other will allways bundle.
> 
> This is interesting.  It sounds like almost the opposite of what I
> expected.  Apparently if the memory requests are large enough that some
> pages are left virtual, you get the Storage_Error.  But if the code
> results in every page allocated being 'touched' you get killed.

Of corse when you read

http://gee.cs.oswego.edu/dl/html/malloc.html

you will see that the OS service of dynamic memory on Unix is rather
primitive - compared to Windows OS/2 and such like.

The principle as I described it still holds however on Unix the program
append new memory to the end and will almost never be able to return memory
to the OS.

Unlike Windows OS/2 where a you can free an unused pages with (Dos)FreeMem.
Of corse I don't know if a particular free () implementation actually
searches for unused pages.

With Regards

Martin
-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com