rhashtable: better high order allocation attempts

When trying to allocate future tables via bucket_table_alloc(), it seems
overkill on large table shifts that we probe for kzalloc() unconditionally
first, as it's likely to fail.

Only probe with kzalloc() for more reasonable table sizes and use vzalloc()
either as a fallback on failure or directly in case of large table sizes.

Fixes: 7e1e776 ("lib: Resizable, Scalable, Concurrent Hash Table")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/rhashtable.c

@@ -217,15 +217,15 @@ static void bucket_table_free(const struct bucket_table *tbl)
 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 					       size_t nbuckets)
 {
-	struct bucket_table *tbl;
+	struct bucket_table *tbl = NULL;
 	size_t size;
 	int i;
 
 	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
-	tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
+	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
+		tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
 	if (tbl == NULL)
 		tbl = vzalloc(size);
-
 	if (tbl == NULL)
 		return NULL;