On Tue 30-10-18 18:47:43, Tetsuo Handa wrote: > 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); > >>> } > >>> vm_unacct_memory(nr_accounted); > >>> + > >>> + /* > >>> + * 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. But MMF_OOF_SKIP is set after we are done with remove_vma. In fact it is the very last thing in exit_mmap. So I do not follow what you mean. -- Michal Hocko SUSE Labs
