Re: Re: Re: [PATCH v4] mm: oom: introduce cpuset oom

[Gang Li]

On 2023/4/11 21:12, Michal Hocko wrote:
> 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.

Yes I can :) It's much easier.

> > > 	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.