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  */
  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 */