nvdimm: reduce duplicated wpq flushes

Existing implemenetation writes to all the flush hint addresses for a
given ND region. This is not necessary as the flushes are per imc and
not per DIMM. Search the mappings and clear out the duplicates at init
to avoid multiple flush to the same imc.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/region_devs.c

@@ -70,7 +70,7 @@ static int nvdimm_map_flush(struct device *dev, struct nvdimm *nvdimm, int dimm,
 
 int nd_region_activate(struct nd_region *nd_region)
 {
-	int i, num_flush = 0;
+	int i, j, num_flush = 0;
 	struct nd_region_data *ndrd;
 	struct device *dev = &nd_region->dev;
 	size_t flush_data_size = sizeof(void *);
@@ -107,6 +107,21 @@ int nd_region_activate(struct nd_region *nd_region)
 			return rc;
 	}
 
+	/*
+	 * Clear out entries that are duplicates. This should prevent the
+	 * extra flushings.
+	 */
+	for (i = 0; i < nd_region->ndr_mappings - 1; i++) {
+		/* ignore if NULL already */
+		if (!ndrd_get_flush_wpq(ndrd, i, 0))
+			continue;
+
+		for (j = i + 1; j < nd_region->ndr_mappings; j++)
+			if (ndrd_get_flush_wpq(ndrd, i, 0) ==
+			    ndrd_get_flush_wpq(ndrd, j, 0))
+				ndrd_set_flush_wpq(ndrd, j, 0, NULL);
+	}
+
 	return 0;
 }