On Thu 15-06-17 19:53:24, Tetsuo Handa wrote: > 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. An alternative would be to allow reaping and exit_mmap race. The unmap part should just work I guess. We just have to be careful to not race with free_pgtables and that shouldn't be too hard to implement (e.g. (ab)use mmap_sem for write there). I haven't thought that through completely though so I might miss something of course. -- Michal Hocko SUSE Labs -- 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>
