target/rd: T10-Dif: RAM disk is allocating more space than required.

Ram disk is allocating 8x more space than required for diff data.
For large RAM disk test, there is small potential for memory
starvation.

(Use block_size when calculating total_sg_needed - sagi + nab)

Signed-off-by: Giridhar Malavali <[e-mail]>
Signed-off-by: Quinn Tran <[e-mail]>
Cc: <[e-mail]> #3.14+
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/target_core_rd.c

···
 	rd_dev->sg_prot_count = 0;
 }
 
-static int rd_build_prot_space(struct rd_dev *rd_dev, int prot_length)
+static int rd_build_prot_space(struct rd_dev *rd_dev, int prot_length, int block_size)
 {
 	struct rd_dev_sg_table *sg_table;
 	u32 total_sg_needed, sg_tables;
···
 
 	if (rd_dev->rd_flags & RDF_NULLIO)
 		return 0;
-
-	total_sg_needed = rd_dev->rd_page_count / prot_length;
+	/*
+	 * prot_length=8byte dif data
+	 * tot sg needed = rd_page_count * (PGSZ/block_size) *
+	 * 		   (prot_length/block_size) + pad
+	 * PGSZ canceled each other.
+	 */
+	total_sg_needed = (rd_dev->rd_page_count * prot_length / block_size) + 1;
 
 	sg_tables = (total_sg_needed / max_sg_per_table) + 1;
 
···
         if (!dev->dev_attrib.pi_prot_type)
 		return 0;
 
-	return rd_build_prot_space(rd_dev, dev->prot_length);
+	return rd_build_prot_space(rd_dev, dev->prot_length,
+				   dev->dev_attrib.block_size);
 }
 
 static void rd_free_prot(struct se_device *dev)