1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_GENERIC_GETORDER_H
3 #define __ASM_GENERIC_GETORDER_H
4 
5 #ifndef __ASSEMBLY__
6 
7 #include <linux/compiler.h>
8 #include <linux/log2.h>
9 
10 /**
11  * get_order - Determine the allocation order of a memory size
12  * @size: The size for which to get the order
13  *
14  * Determine the allocation order of a particular sized block of memory.  This
15  * is on a logarithmic scale, where:
16  *
17  *	0 -> 2^0 * PAGE_SIZE and below
18  *	1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
19  *	2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
20  *	3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
21  *	4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
22  *	...
23  *
24  * The order returned is used to find the smallest allocation granule required
25  * to hold an object of the specified size.
26  *
27  * The result is undefined if the size is 0.
28  */
29 static __always_inline __attribute_const__ int get_order(unsigned long size)
30 {
31 	if (__builtin_constant_p(size)) {
32 		if (!size)
33 			return BITS_PER_LONG - PAGE_SHIFT;
34 
35 		if (size < (1UL << PAGE_SHIFT))
36 			return 0;
37 
38 		return ilog2((size) - 1) - PAGE_SHIFT + 1;
39 	}
40 
41 	size--;
42 	size >>= PAGE_SHIFT;
43 #if BITS_PER_LONG == 32
44 	return fls(size);
45 #else
46 	return fls64(size);
47 #endif
48 }
49 
50 #endif	/* __ASSEMBLY__ */
51 
52 #endif	/* __ASM_GENERIC_GETORDER_H */
53