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Add kernel version numbers for MAP_32BIT. 

Add some details on MAP_32BIT (see http://lwn.net/Articles/294642).
This commit is contained in:
Michael Kerrisk 2008-08-21 04:14:14 +00:00
parent 1d0ab60002
commit c368e7ca76
1 changed files with 12 additions and 3 deletions
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15
man2/mmap.2
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@ -135,12 +135,21 @@ Both of these flags are described in POSIX.1-2001.
In addition, zero or more of the following values can be ORed in
.IR flags :
.TP
.BR MAP_32BIT " (since Linux 2.4.20, 2.6)"
Put the mapping into the first 2 Gigabytes of the process address space.
This flag is only supported on x86-64, for 64-bit programs.
It was added to allow thread stacks to be allocated somewhere
in the first 2GB of memory,
so as to improve context-switch performance on some early
64-bit processors.
.\" See http://lwn.net/Articles/294642 "Tangled up in threads", 19 Aug 08
Modern x86-64 processors no longer have this performance problem,
so use of this flag is not required on those systems.
The
.B MAP_32BIT
Put the mapping into the first 2GB of the process address space.
Ignored when
flag is ignored when
.B MAP_FIXED
is set.
This flag is currently only supported on x86-64, for 64-bit programs.
.TP
.B MAP_ANON
Synonym for