> This a complete rewrite of the oom killer's badness() heuristic which is > used to determine which task to kill in oom conditions. The goal is to > make it as simple and predictable as possible so the results are better > understood and we end up killing the task which will lead to the most > memory freeing while still respecting the fine-tuning from userspace. > > The baseline for the heuristic is a proportion of memory that each task is > currently using in memory plus swap compared to the amount of "allowable" > memory. "Allowable," in this sense, means the system-wide resources for > unconstrained oom conditions, the set of mempolicy nodes, the mems > attached to current's cpuset, or a memory controller's limit. The > proportion is given on a scale of 0 (never kill) to 1000 (always kill), > roughly meaning that if a task has a badness() score of 500 that the task > consumes approximately 50% of allowable memory resident in RAM or in swap > space. > > The proportion is always relative to the amount of "allowable" memory and > not the total amount of RAM systemwide so that mempolicies and cpusets may > operate in isolation; they shall not need to know the true size of the > machine on which they are running if they are bound to a specific set of > nodes or mems, respectively. > > Root tasks are given 3% extra memory just like __vm_enough_memory() > provides in LSMs. In the event of two tasks consuming similar amounts of > memory, it is generally better to save root's task. > > Because of the change in the badness() heuristic's baseline, it is also > necessary to introduce a new user interface to tune it. It's not possible > to redefine the meaning of /proc/pid/oom_adj with a new scale since the > ABI cannot be changed for backward compatability. Instead, a new tunable, > /proc/pid/oom_score_adj, is added that ranges from -1000 to +1000. It may > be used to polarize the heuristic such that certain tasks are never > considered for oom kill while others may always be considered. The value > is added directly into the badness() score so a value of -500, for > example, means to discount 50% of its memory consumption in comparison to > other tasks either on the system, bound to the mempolicy, in the cpuset, > or sharing the same memory controller. > > /proc/pid/oom_adj is changed so that its meaning is rescaled into the > units used by /proc/pid/oom_score_adj, and vice versa. Changing one of > these per-task tunables will rescale the value of the other to an > equivalent meaning. Although /proc/pid/oom_adj was originally defined as > a bitshift on the badness score, it now shares the same linear growth as > /proc/pid/oom_score_adj but with different granularity. This is required > so the ABI is not broken with userspace applications and allows oom_adj to > be deprecated for future removal. > > Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> nack -- 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>