On Fri, May 14, 2021 at 10:52 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Fri, May 14, 2021 at 08:54:47AM -0700, Suren Baghdasaryan wrote:
>
> > Correct, for this function CONFIG_CGROUPS=n and
> > cgroup_disable=pressure are treated the same. True, from the code it's
> > not very obvious. Do you have some refactoring in mind that would make
> > it more explicit?
>
> Does this make sense?
>
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -744,24 +744,26 @@ static void psi_group_change(struct psi_
>
> static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
> {
> + if (cgroup_psi_enabled()) {
> #ifdef CONFIG_CGROUPS
> - struct cgroup *cgroup = NULL;
> + struct cgroup *cgroup = NULL;
>
> - if (!*iter)
> - cgroup = task->cgroups->dfl_cgrp;
> - else if (*iter == &psi_system)
> - return NULL;
> - else
> - cgroup = cgroup_parent(*iter);
> + if (!*iter)
> + cgroup = task->cgroups->dfl_cgrp;
> + else if (*iter == &psi_system)
> + return NULL;
> + else
> + cgroup = cgroup_parent(*iter);
>
> - if (cgroup && cgroup_parent(cgroup)) {
> - *iter = cgroup;
> - return cgroup_psi(cgroup);
> - }
> -#else
> - if (*iter)
> - return NULL;
> + if (cgroup && cgroup_parent(cgroup)) {
> + *iter = cgroup;
> + return cgroup_psi(cgroup);
> + }
> #endif
> + } else {
> + if (*iter)
> + return NULL;
> + }
> *iter = &psi_system;
> return &psi_system;
> }
Hmm. Looks like the case when cgroup_psi_enabled()==true and
CONFIG_CGROUPS=n would miss the "if (*iter) return NULL;" condition.
Effectively with CONFIG_CGROUPS=n this becomes:
if (cgroup_psi_enabled()) { <== assume this is true
#ifdef CONFIG_CGROUPS <== compiled out
#endif
} else {
if (*iter) <== this
statement will never execute
return NULL;
}
*iter = &psi_system;
return &psi_system;
>
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