include/asm-generic/getorder.h

   1 #ifndef __ASM_GENERIC_GETORDER_H
   2 #define __ASM_GENERIC_GETORDER_H
   3
   4 #ifndef __ASSEMBLY__
   5
   6 #include <linux/compiler.h>
   7
   8 /**
   9  * get_order - Determine the allocation order of a memory size
  10  * @size: The size for which to get the order
  11  *
  12  * Determine the allocation order of a particular sized block of memory.  This
  13  * is on a logarithmic scale, where:
  14  *
  15  *      0 -> 2^0 * PAGE_SIZE and below
  16  *      1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
  17  *      2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
  18  *      3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
  19  *      4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
  20  *      ...
  21  *
  22  * The order returned is used to find the smallest allocation granule required
  23  * to hold an object of the specified size.
  24  *
  25  * The result is undefined if the size is 0.
  26  *
  27  * This function may be used to initialise variables with compile time
  28  * evaluations of constants.
  29  */
  30 static inline __attribute_const__ int get_order(unsigned long size)
  31 {
  32         int order;
  33
  34         size = (size - 1) >> (PAGE_SHIFT - 1);
  35         order = -1;
  36         do {
  37                 size >>= 1;
  38                 order++;
  39         } while (size);
  40         return order;
  41 }
  42
  43 #endif  /* __ASSEMBLY__ */
  44
  45 #endif  /* __ASM_GENERIC_GETORDER_H */