mm: move get_order_from_str() to internal.h

In order to implement a kernel parameter similar to ``thp_anon=`` for
shmem, we'll need the function ``get_order_from_str()``.

Instead of duplicating the function, move the function to a shared
header, in which both mm/shmem.c and mm/huge_memory.c will be able to
use it.

Link: https://lkml.kernel.org/r/20241101165719.1074234-5-mcanal@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: mairacanal

mm/huge_memory.c

@@ -958,26 +958,6 @@ static int __init setup_transparent_hugepage(char *str)
 }
 __setup("transparent_hugepage=", setup_transparent_hugepage);
 
-static inline int get_order_from_str(const char *size_str)
-{
-	unsigned long size;
-	char *endptr;
-	int order;
-
-	size = memparse(size_str, &endptr);
-
-	if (!is_power_of_2(size))
-		goto err;
-	order = get_order(size);
-	if (BIT(order) & ~THP_ORDERS_ALL_ANON)
-		goto err;
-
-	return order;
-err:
-	pr_err("invalid size %s in thp_anon boot parameter\n", size_str);
-	return -EINVAL;
-}
-
 static char str_dup[PAGE_SIZE] __initdata;
 static int __init setup_thp_anon(char *str)
 {
@@ -1007,10 +987,22 @@ static int __init setup_thp_anon(char *str)
 				start_size = strsep(&subtoken, "-");
 				end_size = subtoken;
 
-				start = get_order_from_str(start_size);
-				end = get_order_from_str(end_size);
+				start = get_order_from_str(start_size, THP_ORDERS_ALL_ANON);
+				end = get_order_from_str(end_size, THP_ORDERS_ALL_ANON);
 			} else {
-				start = end = get_order_from_str(subtoken);
+				start_size = end_size = subtoken;
+				start = end = get_order_from_str(subtoken,
+								 THP_ORDERS_ALL_ANON);
+			}
+
+			if (start == -EINVAL) {
+				pr_err("invalid size %s in thp_anon boot parameter\n", start_size);
+				goto err;
+			}
+
+			if (end == -EINVAL) {
+				pr_err("invalid size %s in thp_anon boot parameter\n", end_size);
+				goto err;
 			}
 
 			if (start < 0 || end < 0 || start > end)

mm/internal.h

@@ -1291,6 +1291,28 @@ static inline bool alloc_zeroed(void)
 			&init_on_alloc);
 }
 
+/*
+ * Parses a string with mem suffixes into its order. Useful to parse kernel
+ * parameters.
+ */
+static inline int get_order_from_str(const char *size_str,
+				     unsigned long valid_orders)
+{
+	unsigned long size;
+	char *endptr;
+	int order;
+
+	size = memparse(size_str, &endptr);
+
+	if (!is_power_of_2(size))
+		return -EINVAL;
+	order = get_order(size);
+	if (BIT(order) & ~valid_orders)
+		return -EINVAL;
+
+	return order;
+}
+
 enum {
 	/* mark page accessed */
 	FOLL_TOUCH = 1 << 16,