SHM_ALIGN_MASK
((((addr) + SHM_ALIGN_MASK) & ~SHM_ALIGN_MASK) \
+ (((pgoff) << PAGE_SHIFT) & SHM_ALIGN_MASK))
((addr - (pgoff << PAGE_SHIFT)) & SHM_ALIGN_MASK))
info.align_mask = do_color_align ? (PAGE_MASK & SHM_ALIGN_MASK) : 0;