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 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 */