NFSv4.2/pnfs: Make the layoutstats timer configurable

Allow advanced users to set the layoutstats timer in order to lengthen
or shorten the period between layoutstat transmissions to the server.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1d6f045..30d78b5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2279,6 +2279,15 @@
 			The default parameter value of '0' causes the kernel
 			not to attempt recovery of lost locks.
 
+	nfs4.layoutstats_timer =
+			[NFSv4.2] Change the rate at which the kernel sends
+			layoutstats to the pNFS metadata server.
+
+			Setting this to value to 0 causes the kernel to use
+			whatever value is the default set by the layout
+			driver. A non-zero value sets the minimum interval
+			in seconds between layoutstats transmissions.
+
 	nfsd.nfs4_disable_idmapping=
 			[NFSv4] When set to the default of '1', the NFSv4
 			server will return only numeric uids and gids to