Re: [PATCH 5.15.y] mm/numa: no task_numa_fault() call if PTE is changed

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Aug 21, 2024 at 12:10:17PM -0400, 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).
> 
> Link: https://lkml.kernel.org/r/20240809145906.1513458-2-ziy@nvidia.com
> Fixes: b99a342d4f11 ("NUMA balancing: reduce TLB flush via delaying mapping on hint page fault")
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> Reported-by: "Huang, Ying" <ying.huang@intel.com>
> Closes: https://lore.kernel.org/linux-mm/87zfqfw0yw.fsf@yhuang6-desk2.ccr.corp.intel.com/
> Acked-by: David Hildenbrand <david@redhat.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> (cherry picked from commit 40b760cfd44566bca791c80e0720d70d75382b84)
> ---
>  mm/memory.c | 29 ++++++++++++++---------------
>  1 file changed, 14 insertions(+), 15 deletions(-)

All now queued up, thanks.

greg k-h