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Re: SPARSE files considered harmful - please revert
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-
Lapo 'Raist' Luchini
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