start -= start % CPU_PAGE_SIZE;
len = ALIGN_TO(len, CPU_PAGE_SIZE);
if (msync(q->mmap_data + start, len, MS_ASYNC | MS_INVALIDATE) < 0)
start -= start % CPU_PAGE_SIZE;
len = ALIGN_TO(len, CPU_PAGE_SIZE);
if (msync(q->mmap_data + start, len, MS_ASYNC | MS_INVALIDATE) < 0)