On Fri 20-02-15 21:20:58, Tetsuo Handa wrote: > Michal Hocko wrote: > > On Thu 19-02-15 22:29:37, Tetsuo Handa wrote: > > > Michal Hocko wrote: > > > > On Thu 19-02-15 06:01:24, Johannes Weiner wrote: > > > > [...] > > > > > Preferrably, we'd get rid of all nofail allocations and replace them > > > > > with preallocated reserves. But this is not going to happen anytime > > > > > soon, so what other option do we have than resolving this on the OOM > > > > > killer side? > > > > > > > > As I've mentioned in other email, we might give GFP_NOFAIL allocator > > > > access to memory reserves (by giving it __GFP_HIGH). This is still not a > > > > 100% solution because reserves could get depleted but this risk is there > > > > even with multiple oom victims. I would still argue that this would be a > > > > better approach because selecting more victims might hit pathological > > > > case more easily (other victims might be blocked on the very same lock > > > > e.g.). > > > > > > > Does "multiple OOM victims" mean "select next if first does not die"? > > > Then, I think my timeout patch http://marc.info/?l=linux-mm&m=142002495532320&w=2 > > > does not deplete memory reserves. ;-) > > > > It doesn't because > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -2603,9 +2603,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > alloc_flags |= ALLOC_NO_WATERMARKS; > > else if (in_serving_softirq() && (current->flags & PF_MEMALLOC)) > > alloc_flags |= ALLOC_NO_WATERMARKS; > > - else if (!in_interrupt() && > > - ((current->flags & PF_MEMALLOC) || > > - unlikely(test_thread_flag(TIF_MEMDIE)))) > > + else if (!in_interrupt() && (current->flags & PF_MEMALLOC)) > > alloc_flags |= ALLOC_NO_WATERMARKS; > > > > you disabled the TIF_MEMDIE heuristic and use it only for OOM exclusion > > and break out from the allocator. Exiting task might need a memory to do > > so and you make all those allocations fail basically. How do you know > > this is not going to blow up? > > > > Well, treat exiting tasks to imply __GFP_NOFAIL for clean up? > > We cannot determine correct task to kill + allow access to memory reserves > based on lock dependency. Therefore, this patch evenly allow no tasks to > access to memory reserves. > > Exiting task might need some memory to exit, and not allowing access to > memory reserves can retard exit of that task. But that task will eventually > get memory released by other tasks killed by timeout-based kill-more > mechanism. If no more killable tasks or expired panic-timeout, it is > the same result with depletion of memory reserves. > > I think that this situation (automatically making forward progress as if > the administrator is periodically doing SysRq-f until the OOM condition > is solved, or is doing SysRq-c if no more killable tasks or stalled too > long) is better than current situation (not making forward progress since > the exiting task cannot exit due to lock dependency, caused by failing to > determine correct task to kill + allow access to memory reserves). If you really believe this is an improvement then send a proper patch with justification. But I am _really_ skeptical about such a change to be honest. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
