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Date: Sun, 13 Aug 2006 11:23:16 +0200
From: Reini Urban <rurban AT x-ray DOT at>
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Subject: Re: reproducible cygwin memory problems
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Corinna Vinschen schrieb:
...
> Ok, back to mmap/munmap.  Private anonymous mappings are implemented in
> Cygwin by calling VirtualAlloc/VirtualFree.  However, due to
> restrictions in the Win32 API, VirtualFree is only called by munmap, as
> soon as *all* pages within a single mmap'ed area are free'ed by this or
> preceding calls to munmap.
> 
> In other words, the mmap'ed memory will not be returned to the OS, if
> not the complete mmap'ed area is munmap'ed.  Therefore I assume that the
> implementation in Lisp keeps bits of memory around which are not
> munmap'ed for some internal reason.
> 
> Of course it's also possible that there's a bug in Cygwin related to the
> way mmap/munmap is called.  But I have so far no evidence for that and
> simple mmap/munmap tests show that VirtualFree is called as soon as all
> pages in a mmap'ed area have been munmap'ed.  If somebody thinks there's
> a bug in this implementation, please send a simple, self-contained
> testcase in pure C source code, which allows to reproduce the problem.
> Of course, patches are welcome, too :)

And there's the known mmap() under cygwin limitation, esp. harmful to 
clisp, that mmap() can only be properly aligned to a base address modulo 
64k (windows "allocation  granularity"), and not the usual pagesize, if 
it's 4k or 8k. windows pagesize is still 4k though.

http://www.cygwin.com/ml/cygwin/2000-09/msg00380.html
http://www.cygwin.com/ml/cygwin/2004-09/msg00741.html

This has nothing directly to do with the possible xemacs munmap() 
problem, but maybe there's a logic flaw somewhere.
-- 
Reini Urban
http://phpwiki.org/  http://murbreak.at/
http://helsinki.at/  http://spacemovie.mur.at/

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