Re: [PATCH v8 3/3] mm/oom_kill: The OOM reaper traverses the VMA maple tree in reverse order

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Sep 9, 2025 at 2:07 AM zhongjinji <zhongjinji@honor.com> wrote:
>
> Although the oom_reaper is delayed and it gives the oom victim chance to
> clean up its address space this might take a while especially for
> processes with a large address space footprint. In those cases
> oom_reaper might start racing with the dying task and compete for shared
> resources - e.g. page table lock contention has been observed.
>
> Reduce those races by reaping the oom victim from the other end of the
> address space.
>
> It is also a significant improvement for process_mrelease(). When a process
> is killed, process_mrelease is used to reap the killed process and often
> runs concurrently with the dying task. The test data shows that after
> applying the patch, lock contention is greatly reduced during the procedure
> of reaping the killed process.
>
> The test is based on arm64.
>
> Without the patch:
> |--99.57%-- oom_reaper
> |    |--0.28%-- [hit in function]
> |    |--73.58%-- unmap_page_range
> |    |    |--8.67%-- [hit in function]
> |    |    |--41.59%-- __pte_offset_map_lock
> |    |    |--29.47%-- folio_remove_rmap_ptes
> |    |    |--16.11%-- tlb_flush_mmu
> |    |    |--1.66%-- folio_mark_accessed
> |    |    |--0.74%-- free_swap_and_cache_nr
> |    |    |--0.69%-- __tlb_remove_folio_pages
> |    |--19.94%-- tlb_finish_mmu
> |    |--3.21%-- folio_remove_rmap_ptes
> |    |--1.16%-- __tlb_remove_folio_pages
> |    |--1.16%-- folio_mark_accessed
> |    |--0.36%-- __pte_offset_map_lock
>
> With the patch:
> |--99.53%-- oom_reaper
> |    |--55.77%-- unmap_page_range
> |    |    |--20.49%-- [hit in function]
> |    |    |--58.30%-- folio_remove_rmap_ptes
> |    |    |--11.48%-- tlb_flush_mmu
> |    |    |--3.33%-- folio_mark_accessed
> |    |    |--2.65%-- __tlb_remove_folio_pages
> |    |    |--1.37%-- _raw_spin_lock
> |    |    |--0.68%-- __mod_lruvec_page_state
> |    |    |--0.51%-- __pte_offset_map_lock
> |    |--32.21%-- tlb_finish_mmu
> |    |--6.93%-- folio_remove_rmap_ptes
> |    |--1.90%-- __tlb_remove_folio_pages
> |    |--1.55%-- folio_mark_accessed
> |    |--0.69%-- __pte_offset_map_lock
>
> Signed-off-by: zhongjinji <zhongjinji@honor.com>
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Suren Baghdsaryan <surenb@google.com>

> ---
>  mm/oom_kill.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ffa50a1f0132..52d285da5ba4 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -516,7 +516,7 @@ static bool __oom_reap_task_mm(struct mm_struct *mm)
>  {
>         struct vm_area_struct *vma;
>         bool ret = true;
> -       VMA_ITERATOR(vmi, mm, 0);
> +       MA_STATE(mas, &mm->mm_mt, ULONG_MAX, ULONG_MAX);
>
>         /*
>          * Tell all users of get_user/copy_from_user etc... that the content
> @@ -526,7 +526,13 @@ static bool __oom_reap_task_mm(struct mm_struct *mm)
>          */
>         set_bit(MMF_UNSTABLE, &mm->flags);
>
> -       for_each_vma(vmi, vma) {
> +       /*
> +        * It might start racing with the dying task and compete for shared
> +        * resources - e.g. page table lock contention has been observed.
> +        * Reduce those races by reaping the oom victim from the other end
> +        * of the address space.
> +        */
> +       mas_for_each_rev(&mas, vma, 0) {
>                 if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP))
>                         continue;
>
> --
> 2.17.1
>