Re: [PATCH v3 1/3] mm/numa: no task_numa_fault() call if PTE is changed

[David Hildenbrand]

On 09.08.24 16:59, Zi Yan wrote:
> When handling a numa page fault, task_numa_fault() should be called by a
> process that restores the page table of the faulted folio to avoid
> duplicated stats counting. Commit b99a342d4f11 ("NUMA balancing: reduce
> TLB flush via delaying mapping on hint page fault") restructured
> do_numa_page() and did not avoid task_numa_fault() call in the second page
> table check after a numa migration failure. Fix it by making all
> !pte_same() return immediately.
>
> This issue can cause task_numa_fault() being called more than necessary
> and lead to unexpected numa balancing results (It is hard to tell whether
> the issue will cause positive or negative performance impact due to
> duplicated numa fault counting).
>
> Reported-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Closes: https://lore.kernel.org/linux-mm/87zfqfw0yw.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> Fixes: b99a342d4f11 ("NUMA balancing: reduce TLB flush via delaying mapping on hint page fault")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb