BIO_POOL_BITS     139 include/linux/blk_types.h #define BIO_POOL_NONE		((1UL << BIO_POOL_BITS) - 1)
BIO_POOL_BITS     140 include/linux/blk_types.h #define BIO_POOL_OFFSET		(BITS_PER_LONG - BIO_POOL_BITS)