Messages in this thread | | | Date | Thu, 17 Dec 2009 14:21:49 -0800 (PST) | From | David Rientjes <> | Subject | Re: [BUGFIX][PATCH] oom-kill: fix NUMA consraint check with nodemask v4.2 |
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On Tue, 15 Dec 2009, KOSAKI Motohiro wrote:
> > A few requirements that I have: > > Um, good analysis! really. > > > > > - we must be able to define when a task is a memory hogger; this is > > currently done by /proc/pid/oom_adj relying on the overall total_vm > > size of the task as a baseline. Most users should have a good sense > > of when their task is using more memory than expected and killing a > > memory leaker should always be the optimal oom killer result. A better > > set of units other than a shift on total_vm would be helpful, though. > > nit: What's mean "Most users"? desktop user(one of most majority users) > don't have any expection of memory usage. > > but, if admin have memory expection, they should be able to tune > optimal oom result. > > I think you pointed right thing. >
This is mostly referring to production server users where memory consumption by particular applications can be estimated, which allows the kernel to determine when a task is using a wildly unexpected amount that happens to become egregious enough to force the oom killer into killing a task.
That is contrast to using rss as a baseline where we prefer on killing the application with the most resident RAM. It is not always ideal to kill a task with 8GB of rss when we fail to allocate a single page for a low priority task.
> > - we must prefer tasks that run on a cpuset or mempolicy's nodes if the > > oom condition is constrained by that cpuset or mempolicy and its not a > > system-wide issue. > > agreed. (who disagree it?) >
It's possible to nullify the current penalization in the badness heuristic (order 3 reduction) if a candidate task does not share nodes with current's allowed set either by way of cpusets or mempolicies. For example, an oom caused by an application with an MPOL_BIND on a single node can easily kill a task that has no memory resident on that node if its usage (or rss) is 3 orders higher than any candidate that is allowed on my bound node.
> > - we must be able to polarize the badness heuristic to always select a > > particular task is if its very low priority or disable oom killing for > > a task if its must-run. > > Probably I haven't catch your point. What's mean "polarize"? Can you > please describe more? >
We need to be able to polarize tasks so they are always killed regardless of any kernel heuristic (/proc/pid/oom_adj of +15, currently) or always chosen last (-16, currently). We also need a way of completely disabling oom killing for certain tasks such as with OOM_DISABLE.
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