Re: [RFC PATCH v2 3/3] mm, oom: hand over MMF_OOM_SKIP to exit path if it is guranteed to finish
From: Tetsuo Handa
Date: Tue Oct 30 2018 - 05:48:06 EST
On 2018/10/30 15:31, Michal Hocko wrote:
> On Tue 30-10-18 13:45:22, Tetsuo Handa wrote:
>> Michal Hocko wrote:
>>> @@ -3156,6 +3166,13 @@ void exit_mmap(struct mm_struct *mm)
>>> vma = remove_vma(vma);
>>> + /*
>>> + * Now that the full address space is torn down, make sure the
>>> + * OOM killer skips over this task
>>> + */
>>> + if (oom)
>>> + set_bit(MMF_OOM_SKIP, &mm->flags);
>>> /* Insert vm structure into process list sorted by address
>> I don't like setting MMF_OOF_SKIP after remove_vma() loop. 50 users might
>> call vma->vm_ops->close() from remove_vma(). Some of them are doing fs
>> writeback, some of them might be doing GFP_KERNEL allocation from
>> vma->vm_ops->open() with a lock also held by vma->vm_ops->close().
>> I don't think that waiting for completion of remove_vma() loop is safe.
> What do you mean by 'safe' here?
safe = "Does not cause OOM lockup."
remove_vma() is allowed to sleep, and some users might depend on memory
allocation when the OOM killer is waiting for remove_vma() to complete.