On 2023/4/11 20:23, Michal Koutný wrote:
Hello. On Tue, Apr 11, 2023 at 02:58:15PM +0800, Gang Li <ligang.bdlg@xxxxxxxxxxxxx> wrote:+ cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) { + if (nodes_equal(cs->mems_allowed, task_cs(current)->mems_allowed)) { + css_task_iter_start(&(cs->css), CSS_TASK_ITER_PROCS, &it); + while (!ret && (task = css_task_iter_next(&it))) + ret = fn(task, arg); + css_task_iter_end(&it); + } + } + rcu_read_unlock(); + cpuset_read_unlock(); + return ret; +}I see this traverses all cpusets without the hierarchy actually mattering that much. Wouldn't the CONSTRAINT_CPUSET better achieved by globally (or per-memcg) scanning all processes and filtering with:
Oh I see, you mean scanning all processes in all cpusets and scanning all processes globally are equivalent.
nodes_intersect(current->mems_allowed, p->mems_allowed
Perhaps it would be better to use nodes_equal first, and if no suitable victim is found, then downgrade to nodes_intersect? NUMA balancing mechanism tends to keep memory on the same NUMA node, and if the selected victim's memory happens to be on a node that does not intersect with the current process's node, we still won't be able to free up any memory. In this example: A->mems_allowed: 0,1 B->mems_allowed: 1,2 nodes_intersect(A->mems_allowed, B->mems_allowed) == true Memory Distribution: +=======+=======+=======+ | Node0 | Node1 | Node2 | +=======+=======+=======+ | A | | | +-------+-------+-------+ | | |B | +-------+-------+-------+ Process A invoke oom, then kill B. But A still can't get any free mem on Node0 and 1.
(`current` triggers the OOM, `p` is the iterated task) ? Thanks, Michal
