In ll_direct_IO_26() it implements a MAX_DIO_SIZE limit for O_DIRECT requests, based on the previous 128kB kmalloc() limit. However, the underlying code was changed to use OBD_ALLOC_LARGE() and can handle arbitrarily large allocations with vmalloc. Increase the limit from 22MB (128kB kmalloc limit) to 512MB (actually 682MB, just below 4MB new kmalloc limit, and arbitrary with vmalloc).