On Fri 25-08-17 11:39:51, Roman Gushchin wrote: > On Fri, Aug 25, 2017 at 10:14:03AM +0200, Michal Hocko wrote: > > On Thu 24-08-17 15:58:01, Roman Gushchin wrote: > > > On Thu, Aug 24, 2017 at 04:13:37PM +0200, Michal Hocko wrote: > > > > On Thu 24-08-17 14:58:42, Roman Gushchin wrote: > > [...] > > > > > Both ways are not ideal, and sum of the processes is not ideal too. > > > > > Especially, if you take oom_score_adj into account. Will you respect it? > > > > > > > > Yes, and I do not see any reason why we shouldn't. > > > > > > It makes things even more complicated. > > > Right now task's oom_score can be in (~ -total_memory, ~ +2*total_memory) range, > > > and it you're starting summing it, it can be multiplied by number of tasks... > > > Weird. > > > > oom_score_adj is just a normalized bias so if tasks inside oom will use > > it the whole memcg will get accumulated bias from all such tasks so it > > is not completely off. I agree that the more tasks use the bias the more > > biased the whole memcg will be. This might or might not be a problem. > > As you are trying to reimplement the existing oom killer implementation > > I do not think we cannot simply ignore API which people are used to. > > > > If this was a configurable oom policy then I could see how ignoring > > oom_score_adj is acceptable because it would be an explicit opt-in. > > > > > It also will be different in case of system and memcg-wide OOM. > > > > Why, we do honor oom_score_adj for the memcg OOM now and in fact the > > kernel memcg OOM killer shouldn't be very much different from the global > > one except for the tasks scope. > > Assume, you have two tasks (2Gb and 1Gb) in a cgroup with limit 3Gb. > The second task has oom_score_adj +100. Total memory is 64Gb, for example. > > I case of memcg-wide oom first task will be selected; > in case of system-wide OOM - the second. > > Personally I don't like this, but it looks like we have to respect > oom_score_adj set to -1000, I'll alter my patch. I cannot say I would love how oom_score_adj works but it's been like that for a long time and people do rely on that. So we cannot simply change it under people feets. > > > > > I've started actually with such approach, but then found it weird. > > > > > > > > > > > Besides that you have > > > > > > to check each task for over-killing anyway. So I do not see any > > > > > > performance merits here. > > > > > > > > > > It's an implementation detail, and we can hopefully get rid of it at some point. > > > > > > > > Well, we might do some estimations and ignore oom scopes but I that > > > > sounds really complicated and error prone. Unless we have anything like > > > > that then I would start from tasks and build up the necessary to make a > > > > decision at the higher level. > > > > > > Seriously speaking, do you have an example, when summing per-process > > > oom_score will work better? > > > > The primary reason I am pushing for this is to have the common iterator > > code path (which we have since Vladimir has unified memcg and global oom > > paths) and only parametrize the value calculation and victim selection. > > I agree, but I'm not sure that we can (and have to) totally unify the way, > how oom_score is calculated for processes and cgroups. > > But I'd like to see an unified oom_priority approach. This will allow > to define an OOM killing order in a clear way, and use size-based tiebreaking > for items of the same priority. Root-cgroup processes will be compared with > other memory consumers by oom_priority first and oom_score afterwards. This again changes the existing semantic so I really thing we should be careful and this all should be opt-in. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
