nfsd41: hard page limit for DRC

Use no more than 1/128th of the number of free pages at nfsd startup for the
v4.1 DRC.

This is an arbitrary default which should probably end up under the control
of an administrator.

Signed-off-by: Andy Adamson <andros@netapp.com>
[moved added fields in struct svc_serv under CONFIG_NFSD_V4_1]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
[fix set_max_drc calculation of sv_drc_max_pages]
[moved NFSD_DRC_SIZE_SHIFT's declaration up in header file]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

include/linux/nfsd/nfsd.h

@@ -331,6 +331,9 @@ extern struct timeval	nfssvc_boot;
 #define NFSD_LEASE_TIME                 (nfs4_lease_time())
 #define NFSD_LAUNDROMAT_MINTIMEOUT      10   /* seconds */
 
+/* The percent of nr_free_buffer_pages used by the V4.1 server DRC */
+#define NFSD_DRC_SIZE_SHIFT	7
+
 /*
  * The following attributes are currently not supported by the NFSv4 server:
  *    ARCHIVE       (deprecated anyway)

include/linux/sunrpc/svc.h

@@ -95,6 +95,8 @@ struct svc_serv {
 	struct module *		sv_module;	/* optional module to count when
 						 * adding threads */
 	svc_thread_fn		sv_function;	/* main function for threads */
+	unsigned int		sv_drc_max_pages; /* Total pages for DRC */
+	unsigned int		sv_drc_pages_used;/* DRC pages used */
 };
 
 /*