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Date: Sat, 24 May 2003 13:38:11 -0400
From: Christopher Faylor <cgf AT redhat DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: SPARSE files considered harmful - please revert
Message-ID: <20030524173811.GA5141@redhat.com>
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On Sat, May 24, 2003 at 09:58:13AM +0200, Lapo Luchini wrote:
>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.
>>
>>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.

And so, my point is proved.

Thanks.  The feature stays.

cgf

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