LXR linux/include/asm-generic/getorder.h

   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 */
  29static 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