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