On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote: | On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote: | > On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote: | > | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote: | > | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote: | > ... | > | > | As far as my observation, RT-function always have some syscall. because pure | > | > | calculation doesn't need deterministic guarantee. But _if_ you are really | > | > | using such priority design. I'm ok maximum NonRT priority instead maximum | > | > | RT priority too. | > | > | > | > I confess I failed to distinguish memcg OOM and system OOM and used "in | > | > case of OOM kill the selected task the faster you can" as the guideline. | > | > If the exit code path is short that shouldn't be a problem. | > | > | > | > Maybe the right way to go would be giving the dying task the biggest | > | > priority inside that memcg to be sure that it will be the next process from | > | > that memcg to be scheduled. Would that be reasonable? | > | | > | Hmm. I can't understand your point. | > | What do you mean failing distinguish memcg and system OOM? | > | | > | We already have been distinguish it by mem_cgroup_out_of_memory. | > | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). | > | So task selected in select_bad_process is one out of memcg's tasks when | > | memcg have a memory pressure. | > | > The approach of giving the highest priority to the dying task makes sense | > in a system wide OOM situation. I though that would also be good for the | > memcg OOM case. | > | > After Balbir Singh's comment, I understand that in a memcg OOM the dying | > task should have a priority just above the priority of the main task of | > that memcg, in order to avoid interfering in the rest of the system. | > | > That is the point where I failed to distinguish between memcg and system OOM. | > | > Should I pursue that new idea of looking for the right priority inside the | > memcg or is it overkill? I really don't have a clear view of the impact of | > a memcg OOM on system performance - don't know if it is better to solve the | > issue sooner (highest RT priority) or leave it to be solved later (highest | > prio on the memcg). I have the impression the general case points to the | > simpler solution. | | I think highest RT proirity ins't good solution. | As I mentiond, Some RT functions don't want to be preempted by other processes | which cause memory pressure. It makes RT task broken. For the RT case, if you reached a system OOM situation, your determinism has already been hurt. If the memcg OOM happens on the same memcg your RT task is - what will probably be the case most of time - again, the determinism has deteriorated. For both these cases, giving the dying task SCHED_FIFO MAX_RT_PRIO-1 means a faster recovery. I don't know what is the system-wide latency effect of a memcg OOM, if any, or if it would affect an RT task running on another memcg. That is the case where a more careful priority selection could be necessary. | On the other hand, normal processes don't have a requirement of RT. | But it isn't a big problem that it lost little time slice, I think. | So how about raising max normal priority? | but I am not sure this is right solution. | Let's listen other's opinion. | I believe Peter have a good idea. Thanks again for helping to discuss this idea. Luis -- [ Luis Claudio R. Goncalves Bass - Gospel - RT ] [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ] -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>