include/asm-generic/page.h

   1 #ifndef _ASM_GENERIC_PAGE_H
   2 #define _ASM_GENERIC_PAGE_H
   3
   4 #ifdef __KERNEL__
   5 #ifndef __ASSEMBLY__
   6
   7 #include <linux/log2.h>
   8
   9 /*
  10  * non-const pure 2^n version of get_order
  11  * - the arch may override these in asm/bitops.h if they can be implemented
  12  *   more efficiently than using the arch log2 routines
  13  * - we use the non-const log2() instead if the arch has defined one suitable
  14  */
  15 #ifndef ARCH_HAS_GET_ORDER
  16 static inline __attribute__((const))
  17 int __get_order(unsigned long size, int page_shift)
  18 {
  19 #if BITS_PER_LONG == 32 && defined(ARCH_HAS_ILOG2_U32)
  20         int order = __ilog2_u32(size) - page_shift;
  21         return order >= 0 ? order : 0;
  22 #elif BITS_PER_LONG == 64 && defined(ARCH_HAS_ILOG2_U64)
  23         int order = __ilog2_u64(size) - page_shift;
  24         return order >= 0 ? order : 0;
  25 #else
  26         int order;
  27
  28         size = (size - 1) >> (page_shift - 1);
  29         order = -1;
  30         do {
  31                 size >>= 1;
  32                 order++;
  33         } while (size);
  34         return order;
  35 #endif
  36 }
  37 #endif
  38
  39 /**
  40  * get_order - calculate log2(pages) to hold a block of the specified size
  41  * @n - size
  42  *
  43  * calculate allocation order based on the current page size
  44  * - this can be used to initialise global variables from constant data
  45  */
  46 #define get_order(n)                                                    \
  47 (                                                                       \
  48         __builtin_constant_p(n) ?                                       \
  49         ((n < (1UL << PAGE_SHIFT)) ? 0 : ilog2(n) - PAGE_SHIFT) :       \
  50         __get_order(n, PAGE_SHIFT)                                      \
  51  )
  52
  53 #endif  /* __ASSEMBLY__ */
  54 #endif  /* __KERNEL__ */
  55
  56 #endif  /* _ASM_GENERIC_PAGE_H */