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SubjectRe: [patch v2 2/2] mm, oom: avoid reaping only for mm's with blockable invalidate callbacks
On Thu 14-12-17 13:31:00, David Rientjes wrote:
> This uses the new annotation to determine if an mm has mmu notifiers with
> blockable invalidate range callbacks to avoid oom reaping. Otherwise, the
> callbacks are used around unmap_page_range().

Do you have any example where this helped? KVM guest oom killed I guess?

> Signed-off-by: David Rientjes <rientjes@google.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/oom_kill.c | 21 +++++++++++----------
> 1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -514,15 +514,12 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
> }
>
> /*
> - * If the mm has notifiers then we would need to invalidate them around
> - * unmap_page_range and that is risky because notifiers can sleep and
> - * what they do is basically undeterministic. So let's have a short
> + * If the mm has invalidate_{start,end}() notifiers that could block,
> * sleep to give the oom victim some more time.
> * TODO: we really want to get rid of this ugly hack and make sure that
> - * notifiers cannot block for unbounded amount of time and add
> - * mmu_notifier_invalidate_range_{start,end} around unmap_page_range
> + * notifiers cannot block for unbounded amount of time
> */
> - if (mm_has_notifiers(mm)) {
> + if (mm_has_blockable_invalidate_notifiers(mm)) {
> up_read(&mm->mmap_sem);
> schedule_timeout_idle(HZ);
> goto unlock_oom;
> @@ -565,10 +562,14 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
> * count elevated without a good reason.
> */
> if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
> - tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
> - unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
> - NULL);
> - tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
> + const unsigned long start = vma->vm_start;
> + const unsigned long end = vma->vm_end;
> +
> + tlb_gather_mmu(&tlb, mm, start, end);
> + mmu_notifier_invalidate_range_start(mm, start, end);
> + unmap_page_range(&tlb, vma, start, end, NULL);
> + mmu_notifier_invalidate_range_end(mm, start, end);
> + tlb_finish_mmu(&tlb, start, end);
> }
> }
> pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",

--
Michal Hocko
SUSE Labs

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