lib/rhashtable.c: use kvzalloc() in bucket_table_alloc() when possible

bucket_table_alloc() can be currently called with GFP_KERNEL or
GFP_ATOMIC. For the former we basically have an open coded kvzalloc()
while the later only uses kzalloc(). Let's simplify the code a bit by
the dropping the open coded path and replace it with kvzalloc().

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Michal Hocko <[e-mail]>
Cc: Thomas Graf <[e-mail]>
Cc: Herbert Xu <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/rhashtable.c

···
 	int i;
 
 	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
-	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
-	    gfp != GFP_KERNEL)
+	if (gfp != GFP_KERNEL)
 		tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
-	if (tbl == NULL && gfp == GFP_KERNEL)
-		tbl = vzalloc(size);
+	else
+		tbl = kvzalloc(size, gfp);
 
 	size = nbuckets;