int __get_order(unsigned long size)

2017-12-6 10:26:50
4.9.51
int __get_order(unsigned long size)
{
int order;

size--;
   size >>= PAGE_SHIFT;
#if BITS_PER_LONG == 32
   order = fls(size);
#else
   order = fls64(size);
#endif
   return order;
}

1.3.100 __get_order@drivers/block/floppy.c

*/
/* Pure 2^n version of get_order */
static inline int __get_order(unsigned long size)
{
int order;

size = (size-1) >> (PAGE_SHIFT-1);
   order = -1;
   do {
       size >>= 1;
       order++;
   } while (size);
   return order;
}

注：返回值order
块系数k以2为底的对数，[0, NR_MEM_LISTS]
块大小：PAGE_SIZE*k
计算order: order = log2k, k=2^n, 则order=n

k=1 n=0
   k=2 n=1
   k=4 n=2
   k=8 n=3
   k=16 n=4
   k=32 n=5

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