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 9:29 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> 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>

Apparently I misspelled my own last name :)

Reviewed-by: Suren Baghdasaryan <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
> >