ipc: document the new auto_msgmni proc file

Update Documentation/filesystems/proc.txt: it describes the file
auto_msgmni intoduced to enable/disable msgmni automatic recomputing upon
memory add/remove (see thread http://lkml.org/lkml/2008/7/4/27).  Also
added a description for msgmni (this filex is only listed in
Documentation/sysctl/kernel.txt).

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/proc.txt

@@ -1339,6 +1339,25 @@ Enables/Disables the protection of the per-process proc entries "maps" and
 "smaps".  When enabled, the contents of these files are visible only to
 readers that are allowed to ptrace() the given process.
 
+msgmni
+------
+
+Maximum number of message queue ids on the system.
+This value scales to the amount of lowmem. It is automatically recomputed
+upon memory add/remove or ipc namespace creation/removal.
+When a value is written into this file, msgmni's value becomes fixed, i.e. it
+is not recomputed anymore when one of the above events occurs.
+Use auto_msgmni to change this behavior.
+
+auto_msgmni
+-----------
+
+Enables/Disables automatic recomputing of msgmni upon memory add/remove or
+upon ipc namespace creation/removal (see the msgmni description above).
+Echoing "1" into this file enables msgmni automatic recomputing.
+Echoing "0" turns it off.
+auto_msgmni default value is 1.
+
 
 2.4 /proc/sys/vm - The virtual memory subsystem
 -----------------------------------------------