Michal Hocko wrote: > On Wed 14-06-17 16:43:03, David Rientjes wrote: > > If mm->mm_users is not incremented because it is already zero by the oom > > reaper, meaning the final refcount has been dropped, do not set > > MMF_OOM_SKIP prematurely. > > > > __mmput() may not have had a chance to do exit_mmap() yet, so memory from > > a previous oom victim is still mapped. > > true and do we have a _guarantee_ it will do it? E.g. can somebody block > exit_aio from completing? Or can somebody hold mmap_sem and thus block > ksm_exit resp. khugepaged_exit from completing? The reason why I was > conservative and set such a mm as MMF_OOM_SKIP was because I couldn't > give a definitive answer to those questions. And we really _want_ to > have a guarantee of a forward progress here. Killing an additional > proecess is a price to pay and if that doesn't trigger normall it sounds > like a reasonable compromise to me. Right. If you want this patch, __oom_reap_task_mm() must not return true without setting MMF_OOM_SKIP (in other words, return false if __oom_reap_task_mm() does not set MMF_OOM_SKIP). The most important role of the OOM reaper is to guarantee that the OOM killer is re-enabled within finite time, for __mmput() cannot guarantee that MMF_OOM_SKIP is set within finite time. > > > __mput() naturally requires no > > references on mm->mm_users to do exit_mmap(). > > > > Without this, several processes can be oom killed unnecessarily and the > > oom log can show an abundance of memory available if exit_mmap() is in > > progress at the time the process is skipped. > > Have you seen this happening in the real life? > > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
