clImportMemoryARM Opencl sometime return error -6

I am testing the clImportMemoryARM function of opencl.

env

• android C++
• CPU MTK G99
• GPU: Mali-G57 MC2 r0p1
• EXTENSIONS: cl_khr_global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_byte_addressable_store cl_khr_3d_image_writes cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_fp16 cl_khr_icd cl_khr_egl_image cl_khr_image2d_from_buffer cl_khr_depth_images cl_khr_subgroups cl_khr_subgroup_extended_types cl_khr_subgroup_non_uniform_vote cl_khr_subgroup_ballot cl_khr_il_program cl_khr_priority_hints cl_khr_create_command_queue cl_khr_spirv_no_integer_wrap_decoration cl_khr_extended_versioning cl_khr_device_uuid cl_arm_core_id cl_arm_printf cl_arm_non_uniform_work_group_size cl_arm_import_memory cl_arm_import_memory_dma_buf cl_arm_import_memory_host cl_arm_import_memory_protected cl_arm_import_memory_android_hardware_buffer cl_arm_integer_dot_product_int8 cl_arm_integer_dot_product_accumulate_int8 cl_arm_integer_dot_product_accumulate_saturate_int8 cl_arm_job_slot_selection cl_arm_scheduling_controls cl_arm_controlled_kernel_termination cl_ext_cxx_for_opencl

code

    cl_int error;
    cl_uint num_devices;
    cl_device_id devices[1];
    cl_platform_id platforms[1];
    clGetDeviceIDs(platforms[0], CL_DEVICE_TYPE_GPU, 1, devices, &num_devices);
    cl_context context = clCreateContext( NULL, 1, devices, NULL, NULL, &error );
    cl_command_queue  queue = clCreateCommandQueue(context, devices[0], 0, NULL);
    

    int Length = 1024;
    char *allocptr = (char *)malloc( Length*sizeof(char));

    const cl_import_properties_arm importProperties[] =
    {
            CL_IMPORT_TYPE_ARM,
            CL_IMPORT_TYPE_HOST_ARM,
            0
    };
    cl_mem buffer = clImportMemoryARM( context,
                                         CL_MEM_READ_WRITE,
                                         importProperties,
                                         allocptr,
                                         Length*sizeof(char),
                                         &error );

when length is 1024,sometimes clImportMemoryARM return error -6 which means CL_OUT_OF_HOST_MEMORY,when I set length = 1024x512x2 which fellows khronos/cl_arm_import_memory.txt no error ever occurred. I want know why.

You asked on Arm Community Forums as well, so putting answer you got there here too, for different audience:

This may happen if the pointer you are trying to import is not aligned to the size of a cache line (i.e. 64 bytes). The specification you linked states:

Though the application is free to provide allocations without any specific alignment on coherent systems, there is a requirement to provide pointers aligned to a cache line on systems where there is no HW-managed coherency between CPU and GPU.

You could align the pointer yourself or use a function such as posix_memalign.