vfs: use 'unsigned long' accesses for dcache name comparison and hashing

Ok, this is hacky, and only works on little-endian machines with goo
unaligned handling.  And even then only with CONFIG_DEBUG_PAGEALLOC
disabled, since it can access up to 7 bytes after the pathname.

But it runs like a bat out of hell.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/dcache.c

@@ -144,6 +144,28 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
 static inline int dentry_cmp(const unsigned char *cs, size_t scount,
 				const unsigned char *ct, size_t tcount)
 {
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+	unsigned long a,b,mask;
+
+	if (unlikely(scount != tcount))
+		return 1;
+
+	for (;;) {
+		a = *(unsigned long *)cs;
+		b = *(unsigned long *)ct;
+		if (tcount < sizeof(unsigned long))
+			break;
+		if (unlikely(a != b))
+			return 1;
+		cs += sizeof(unsigned long);
+		ct += sizeof(unsigned long);
+		tcount -= sizeof(unsigned long);
+		if (!tcount)
+			return 0;
+	}
+	mask = ~(~0ul << tcount*8);
+	return unlikely(!!((a ^ b) & mask));
+#else
 	if (scount != tcount)
 		return 1;
 
@@ -155,6 +177,7 @@ static inline int dentry_cmp(const unsigned char *cs, size_t scount,
 		tcount--;
 	} while (tcount);
 	return 0;
+#endif
 }
 
 static void __d_free(struct rcu_head *head)