On Fri, May 14, 2021 at 11:20 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> 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;
>
Ah, sorry. I forgot that CONFIG_CGROUPS=n would force
cgroup_psi_enabled()==false (the way function is defined in cgroup.h),
so (CONFIG_CGROUPS=n && cgroup_psi_enabled()==true) is an invalid
configuration. I think adding a comment to your suggestion would make
it more clear.
So your suggestion seems to work. I'll test it and include it in the
next revision. Thanks!
> >
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> >
