[DRAFT: DONT COMMIT] Enable zero-copy subbuffers across all alloc typ…

[Prithviraj-R]

…es for iGPUs

Details:

Description of the issue (symptom, root-cause, how it was resolved)

• Eliminates redundant weight copies during model loading for integrated GPUs by binding mmap'd cache file memory directly to GPU without intermediate usm_device allocation
• Reduces memory footprint during inference by reusing host memory as GPU-accessible buffers
• Zero-copy enabled when: iGPU, XE2+ architecture, USM host support available
• Falls back gracefully to copy-based path when zero-copy requirements not met

Implementation changes:

• Add ocl_engine::supports_hostbuffer() to validate zero-copy capability (checks for integrated GPU, XE2+ arch, USM host allocation support)
• Add ocl_engine::create_hostbuffer_impl() to bind host memory with CL_MEM_USE_HOST_PTR
• Simplify zero-copy detection in data.hpp load path (remove redundant capability checks)
• Use ib.seek_current_ptr() instead of dummy reads for padding alignment
• Remove is_mmap_tensor_4K_aligned() helpers

Changed files:
src/plugins/intel_gpu/include/intel_gpu/graph/serialization/binary_buffer.hpp src/plugins/intel_gpu/include/intel_gpu/primitives/data.hpp src/plugins/intel_gpu/include/intel_gpu/runtime/device_info.hpp src/plugins/intel_gpu/src/graph/program.cpp
src/plugins/intel_gpu/src/runtime/ocl/ocl_device.cpp src/plugins/intel_gpu/src/runtime/ocl/ocl_engine.cpp src/plugins/intel_gpu/tests/unit/test_cases/cache_serialization_test.cpp

Reproduction step and snapshot (if applicable. Do not attach for customer model) NA

Problematic graph
NA

Checklist

• Is it a proper fix? Yes (memory optimization, not a workaround)
• Did you include test case for this fix, if necessary? NA
• Did you review existing test that can be extended to cover this scenario? NA

Tickets:

• CVS-176160

AI Assistance:

• AI assistance used: yes
• AI was used for code implementation, naming suggestions, and comment refinement.

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