proc.5: Add details for threads-max

Add detail information for threads-max.
The checks for minimum and maximum values exist since kernel 4.1.
https://lkml.org/lkml/2015/3/15/96

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man5/proc.5 b/man5/proc.5
index bb648d4fe98631e961522dbf7056bc1f0d330955..83f30afdd91d8764f2e19eba15a05f9736223a9b 100644 (file)
--- a/man5/proc.5
+++ b/man5/proc.5
@@ -4265,8 +4265,22 @@ this is the fifth kernel built from this source base and the
 date following it indicates the time the kernel was built.
 .TP
 .IR /proc/sys/kernel/threads-max " (since Linux 2.3.11)"
+.\" The following is based on Documentation/sysctl/kernel.txt
 This file specifies the system-wide limit on the number of
 threads (tasks) that can be created on the system.
+
+The minimum value that can be written to threads-max is 20.
+The maximum value that can be written to threads-max is given by the
+constant
+.B FUTEX_TID_MASK
+(0x3fffffff).
+If a value outside of this range is written to threads-max an error
+.B EINVAL
+occurs.
+
+The value written is checked against the available RAM pages.
+If the thread structures would occupy too much (more than 1/8th)
+of the available RAM pages, threads-max is reduced accordingly.
 .TP
 .IR /proc/sys/kernel/zero-paged " (PowerPC only) "
 This file