[Question] get_vma_policy() isn't compatible with {pin, get}_user_pages_remote

[Jinjiang Tu <tujinjiang@huawei.com>]

get_vma_policy() returns the mempolicy for the vma. If the vma has set 
mempolicy, the policy is returned. Otherwise,
call get_task_policy(current) to get the mempolicy of current task. 
However, it isn't reasonable for
pin_user_pages_remote() and get_user_pages_remote() cases.

Assume task A calls pin_user_pages_remote() to pin user pages from task 
B. If the [start, start + nr_pages) isn't
populated with pages, handle_mm_fault() will be called by task A. 
However, if the vma doesn't set memory policy,
the mempolicy of task A instead of task B is used to allocate. It seems 
to be unreasonable. See
dequeue_hugetlb_folio_vma()->huge_node().

We can only obtain mm in get_vma_policy(), but we couldn't get the task, 
since a mm can be associated with multiple
tasks(threads) and the task mempolicy is at thread granularity.

Is this situation reasonable? And if not, how could we fix it?

Thanks.