Re: [RFC PATCH 1/4] mm/mempolicy: Expose policy_nodemask() in include/linux/mempolicy.h

[Huang, Ying]

David Hildenbrand <david@xxxxxxxxxx> writes:

> On 13.06.25 18:33, Bijan Tabatabai wrote:
>> On Fri, Jun 13, 2025 at 8:45 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>>>
>>> On 12.06.25 20:13, Bijan Tabatabai wrote:
>>>> From: Bijan Tabatabai <bijantabatab@xxxxxxxxxx>
>>>>

[snip]

>> I did not use get_vma_policy or mpol_misplaced, which I believe is
>> the
>> closest function that exists for what I want in this patch, because
>> those functions
>
> I think what you mean is, that you are performing an rmap walk. But
> there, you do have a VMA + MM available (stable).
>
>> seem to assume they are called inside of the task that the folio/vma
>> is mapped to.
>
> But, we do have a VMA at hand, so why would we want to ignore any set
> policy? (I think VMA policies so far only apply to shmem, but still).
>
> I really think you want to use get_vma_policy() instead of the task policy.
>
>
>> More specifically, mpol_misplaced assumes it is being called within a
>> page fault.
>> This doesn't work for us, because we call it inside of a kdamond process.
>
> Right.
>
> But it uses the vmf only for ...
>
> 1) Obtaining the VMA
> 2) Sanity-checking that the ptlock is held.

3) update NUMA balancing per-folio cpupid state (via should_numa_migrate_memory()).

This needs to be called by the NUMA page fault handler.

> Which, you also have during the rmap walk.
>

[snip]

---
Best Regards,
Huang, Ying