[BUG] direct io fails in latest version

[hb-lee]

Describe the bug
The main branch runs with direct io configuration, it throws exceptions in write_file.

To Reproduce
Steps to reproduce the behavior:

1. add try... exception in write_file at local_disk_backend.py
2. .enable direct io
3. send the request to store the kv cache
4. write_file throws exceptions.

• OS: [e.g. openEuler]
• CANN Version: 8.3.0
• Ascend HDK Version: 25.3.rc1
• vLLM Version: v0.11.0

Additional context
NA

[chloroethylene]

For now, we can replace ·aclrtMallocHost· with ·mmap· for memory allocation, which avoids triggering the issue. The root cause still needs further investigation.