nfsd41: use globals for DRC limits

The version 4.1 DRC memory limit and tracking variables are server wide and
session specific. Replace struct svc_serv fields with globals.
Stop using the svc_serv sv_lock.

Add a spinlock to serialize access to the DRC limit management variables which
change on session creation and deletion (usage counter) or (future)
administrative action to adjust the total DRC memory limit.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
diff --git a/include/linux/nfsd/nfsd.h b/include/linux/nfsd/nfsd.h
index 2b49d67..2571f85 100644
--- a/include/linux/nfsd/nfsd.h
+++ b/include/linux/nfsd/nfsd.h
@@ -56,6 +56,9 @@
 extern u32			nfsd_supported_minorversion;
 extern struct mutex		nfsd_mutex;
 extern struct svc_serv		*nfsd_serv;
+extern spinlock_t		nfsd_drc_lock;
+extern unsigned int		nfsd_drc_max_pages;
+extern unsigned int		nfsd_drc_pages_used;
 
 extern struct seq_operations nfs_exports_op;