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mdoc(7) police: fix formatting errors in rev 1.27.

This commit is contained in:
Ruslan Ermilov 2000-12-04 08:11:50 +00:00
parent b7f97db312
commit 687a7e07cf
1 changed files with 27 additions and 13 deletions
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40
lib/libc/sys/mmap.2
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@ -169,20 +169,34 @@ maintained whether you use MAP_NOSYNC or not. This option is not portable
across UNIX platforms (yet), though some may implement the same behavior across UNIX platforms (yet), though some may implement the same behavior
by default. by default.
.Pp .Pp
WARNING! Extending a file with ftruncate(), thus creating a big hole, and WARNING!
then filling the hole by modifying a shared mmap() can lead to severe Extending a file with
file fragmentation. In order to avoid such fragmentation you should .Xr ftruncate 2 ,
always pre-allocate the file's backing store by write()ing zero's into the thus creating a big hole, and then filling the hole by modifying a shared
newly extended area prior to modifying the area via your mmap(). .Fn mmap
The fragmentation problem is especially sensitive to MAP_NOSYNC pages, can lead to severe file fragmentation.
because pages may be flushed to disk in a totally random order. In order to avoid such fragmentation you should always pre-allocate the
file's backing store by
.Fn write Ns ing
zero's into the newly extended area prior to modifying the area via your
.Fn mmap .
The fragmentation problem is especially sensitive to
.Dv MAP_NOSYNC
pages, because pages may be flushed to disk in a totally random order.
.Pp .Pp
The same applies when using MAP_NOSYNC to implement a file-based shared The same applies when using
memory store. It is recommended that you create the backing store by .Dv MAP_NOSYNC
write()ing zero's to the backing file rather then ftruncate()ing it. You to implement a file-based shared memory store.
can test file fragmentation by observing the KB/t (kilobytes per transfer) It is recommended that you create the backing store by
results from an 'iostat 1' while reading a large file sequentially, e.g. .Fn write Ns ing
using 'dd if=filename of=/dev/null bs=32k'. zero's to the backing file rather then
.Fn ftruncate Ns ing
it.
You can test file fragmentation by observing the KB/t (kilobytes per
transfer) results from an
.Dq Li iostat 1
while reading a large file sequentially, e.g. using
.Dq Li dd if=filename of=/dev/null bs=32k .
.Pp .Pp
The The
.Xr fsync 2 .Xr fsync 2