[XFS] Switch pagebuf hashing to be based on the block_device address

rather than the dev_t. Should give better distribution. Mod from Al Viro.

SGI Modid: 2.5.x-xfs:slinx:158800a

fs/xfs/pagebuf/page_buf.c

@@ -174,16 +174,13 @@ STATIC pb_hash_t	pbhash[NHASH];
 
 STATIC int
 _bhash(
-	dev_t		dev,
+	struct block_device *bdev,
 	loff_t		base)
 {
 	int		bit, hval;
 
 	base >>= 9;
-	/*
-	 * dev_t is 16 bits, loff_t is always 64 bits
-	 */
-	base ^= dev;
+	base ^= (unsigned long)bdev / L1_CACHE_BYTES;
 	for (bit = hval = 0; base && bit < sizeof(base) * 8; bit += NBITS) {
 		hval ^= (int)base & (NHASH-1);
 		base >>= NBITS;
@@ -619,7 +616,7 @@ _pagebuf_find(				/* find buffer for block	*/
 	/* Ensure we never do IOs that are not sector aligned */
 	BUG_ON(range_base & (loff_t)target->pbr_smask);
 
-	hval = _bhash(target->pbr_bdev->bd_dev, range_base);
+	hval = _bhash(target->pbr_bdev, range_base);
 	h = &pbhash[hval];
 
 	spin_lock(&h->pb_hash_lock);