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>

Documentation/kernel-parameters.txt

@@ -2279,6 +2279,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			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

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -533,14 +533,17 @@ nfs4_ff_layoutstat_start_io(struct nfs4_ff_layout_mirror *mirror,
 			    ktime_t now)
 {
 	static const ktime_t notime = {0};
+	s64 report_interval = FF_LAYOUTSTATS_REPORT_INTERVAL;
 
 	nfs4_ff_start_busy_timer(&layoutstat->busy_timer, now);
 	if (ktime_equal(mirror->start_time, notime))
 		mirror->start_time = now;
 	if (ktime_equal(mirror->last_report_time, notime))
 		mirror->last_report_time = now;
+	if (layoutstats_timer != 0)
+		report_interval = (s64)layoutstats_timer * 1000LL;
 	if (ktime_to_ms(ktime_sub(now, mirror->last_report_time)) >=
-			FF_LAYOUTSTATS_REPORT_INTERVAL) {
+			report_interval) {
 		mirror->last_report_time = now;
 		return true;
 	}

fs/nfs/pnfs.c

@@ -2285,3 +2285,7 @@ pnfs_report_layoutstat(struct inode *inode, gfp_t gfp_flags)
 }
 EXPORT_SYMBOL_GPL(pnfs_report_layoutstat);
 #endif
+
+unsigned int layoutstats_timer;
+module_param(layoutstats_timer, uint, 0644);
+EXPORT_SYMBOL_GPL(layoutstats_timer);

fs/nfs/pnfs.h

@@ -528,12 +528,15 @@ pnfs_use_threshold(struct nfs4_threshold **dst, struct nfs4_threshold *src,
 					nfss->pnfs_curr_ld->id == src->l_type);
 }
 
+extern unsigned int layoutstats_timer;
+
 #ifdef NFS_DEBUG
 void nfs4_print_deviceid(const struct nfs4_deviceid *dev_id);
 #else
 static inline void nfs4_print_deviceid(const struct nfs4_deviceid *dev_id)
 {
 }
+
 #endif /* NFS_DEBUG */
 #else  /* CONFIG_NFS_V4_1 */