On Wed, 3 Feb 2016, Michal Hocko wrote:
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 9a0e4e5f50b4..840e03986497 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -443,13 +443,6 @@ static bool __oom_reap_vmas(struct mm_struct *mm)
> continue;
>
> /*
> - * mlocked VMAs require explicit munlocking before unmap.
> - * Let's keep it simple here and skip such VMAs.
> - */
> - if (vma->vm_flags & VM_LOCKED)
> - continue;
> -
> - /*
> * Only anonymous pages have a good chance to be dropped
> * without additional steps which we cannot afford as we
> * are OOM already.
> @@ -459,9 +452,12 @@ static bool __oom_reap_vmas(struct mm_struct *mm)
> * we do not want to block exit_mmap by keeping mm ref
> * count elevated without a good reason.
> */
> - if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
> + if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
> + if (vma->vm_flags & VM_LOCKED)
> + munlock_vma_pages_all(vma);
> unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
> &details);
> + }
> }
> tlb_finish_mmu(&tlb, 0, -1);
> up_read(&mm->mmap_sem);
Are we concerned about munlock_vma_pages_all() taking lock_page() and
perhaps stalling forever, the same way it would stall in exit_mmap() for
VM_LOCKED vmas, if another thread has locked the same page and is doing an
allocation? I'm wondering if in that case it would be better to do a
best-effort munlock_vma_pages_all() with trylock_page() and just give up
on releasing memory from that particular vma. In that case, there may be
other memory that can be freed with unmap_page_range() that would handle
this livelock.
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