On Wed, 25 Aug 2010 19:50:22 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Thu, 26 Aug 2010, KAMEZAWA Hiroyuki wrote: > > > Hmm. I'll add a text like following to cgroup/memory.txt. O.K. ? > > > > == > > Notes on oom_score and oom_score_adj. > > > > oom_score is calculated as > > oom_score = (taks's proportion of memory) + oom_score_adj. > > > > I'd replace "memory" with "memory limit (or memsw limit)" so it's clear > we're talking about the amount of memory available to task. > ok. > > Then, when you use oom_score_adj to control the order of priority of oom, > > you should know about the amount of memory you can use. > > Hmm, you need to know the amount of memory that you can use iff you know > the memcg limit and it's a static value. Otherwise, you only need to know > the "memory usage of your application relative to others in the same > cgroup." An oom_score_adj of +300 adds 30% of that memcg's limit to the > task, allowing all other tasks to use 30% more memory than that task with > it still be killed. An oom_score_adj of -300 allows that task to use 30% > more memory than other tasks without getting killed. These don't need to > know the actual limit. > Hmm. What's complicated is oom_score_adj's behavior. > > So, an approximate oom_score under memcg can be > > > > memcg_oom_score = (oom_score - oom_score_adj) * system_memory/memcg's limit > > + oom_score_adj. > > > > Right, that's the exact score within the memcg. > > But, I still wouldn't encourage a formula like this because the memcg > limit (or cpuset mems, mempolicy nodes, etc) are dynamic and may change > out from under us. So it's more important to define oom_score_adj in the > user's mind as a proportion of memory available to be added (either > positively or negatively) to its memory use when comparing it to other > tasks. The point is that the memcg limit isn't interesting in this > formula, it's more important to understand the priority of the task > _compared_ to other tasks memory usage in that memcg. > yes. For defineing/understanding priority, oom_score_adj is that. But it's priority isn't static. > It probably would be helpful, though, if you know that a vital system task > uses 1G, for instance, in a 4G memcg that an oom_score_adj of -250 will > disable oom killing for it. yes. > If that tasks leaks memory or becomes > significantly large, for whatever reason, it could be killed, but we _can_ > discount the 1G in comparison to other tasks as the "cost of doing > business" when it comes to vital system tasks: > > (memory usage) * (memory+swap limit / system memory) > yes. under 8G system, -250 will allow ingnoring 2G of usage. == How about this text ? == When you set a task's oom_score_adj, it can get priority not to be oom-killed. oom_score_adj gives priority proportional to the memory limitation. Assuming you set -250 to oom_score_adj. Under 4G memory limit, it gets 25% of bonus...1G memory bonus for avoiding OOM. Under 8G memory limit, it gets 25% of bonus...2G memory bonus for avoiding OOM. Then, what bonus a task can get depends on the context of OOM. If you use oom_score_adj and want to give bonus to a task, setting it in regard with minimum memory limitation which a task is under will work well. == Thanks, -Kame -- 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>