Re: [patch v2 2/2] mm, oom: avoid reaping only for mm's with blockable invalidate callbacks

[Michal Hocko]

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@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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