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semop.2: Note defaults for SEMOPM and warn against increasing > 1000 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-01-29 12:50:11 +01:00
parent 8a3e6dc72f
commit 98f792f704
1 changed files with 15 additions and 3 deletions
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18
man2/semop.2
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@ -459,10 +459,22 @@ call:
.B SEMOPM
Maximum number of operations allowed for one
.BR semop ()
call (32)
(on Linux, this limit can be read and modified via the third field of
.IR /proc/sys/kernel/sem ).
call.
Before Linux 3.19,
.\" commit e843e7d2c88b7db107a86bd2c7145dc715c058f4
the default value for this limit was 32.
Since Linux 3.19, the default value is 500.
On Linux, this limit can be read and modified via the third field of
.IR /proc/sys/kernel/sem .
.\" This /proc file is not available in Linux 2.2 and earlier -- MTK
.IR Note :
this limit should not be raised above 1000,
.\" See comment in Linux 3.19 source file include/uapi/linux/sem.h
because of the risk of that
.BR semop (2)
fails due to kernel memory fragmentation when allocating memory to copy the
.IR sops
array.
.TP
.B SEMVMX
Maximum allowable value for