On Tue 11-04-23 21:04:18, Gang Li wrote:
>
>
> 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.
Why cannot you simple select a process from the cpuset the allocating
process belongs to? I thought the whole idea was to handle well
partitioned workloads.
> > 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?
How can this happen?
> 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.
AFAIR NUMA balancing doesn't touch processes with memory policies.
--
Michal Hocko
SUSE Labs
