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Message-ID: <3ECF2615.4080108@lapo.it>
Date: Sat, 24 May 2003 09:58:13 +0200
From: Lapo Luchini <lapo AT lapo DOT it>
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To: Mailing List: CygWin <cygwin AT cygwin DOT com>
Subject: Re: SPARSE files considered harmful - please revert
References: <16072 DOT 6666 DOT 10124 DOT 338022 AT gargle DOT gargle DOT HOWL> <00f301c31e12$c29efdb0$6400a8c0 AT FoxtrotTech0001> <00be01c31e15$944d0d50$78d96f83 AT pomello> <005601c31e26$77671260$6400a8c0 AT FoxtrotTech0001> <20030519175913 DOT GA24066 AT redhat DOT com> <008001c31e5e$39c0c680$6400a8c0 AT FoxtrotTech0001> <20030520024151 DOT GA1812 AT redhat DOT com> <badft3$9r8$1 AT main DOT gmane DOT org>
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Rolf Campbell wrote:

>> 3) What no one seems to be mentioning is that we are trying to emulate
>> UNIX behavior here.  If the above is an issue for Windows then it could
>> also be an issue for UNIX.
>> cgf
>
> And it is. 

e.g. from FreeBSD 4.8's "man mmap":

   WARNING!  Extending a file with ftruncate(2), thus cre-
   ating a big hole, and then filling the hole by modify-
   ing a shared mmap() can lead to severe file fragmenta-
   tion.  In order to avoid such fragmentation you should
   always pre-allocate the file's backing store by
   write()ing zero's into the newly extended area prior to
   modifying the area via your mmap().  The fragmentation
   problem is especially sensitive to MAP_NOSYNC pages,
   because pages may be flushed to disk in a totally ran-
   dom order.

-- 
Lapo 'Raist' Luchini
lapo AT lapo DOT it (PGP & X.509 keys available)
http://www.lapo.it (ICQ UIN: 529796)



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