Re: [PATCH v3 2/5] mm: kmem: add direct objcg pointer to task_struct

[Shakeel Butt]

On Wed, Oct 18, 2023 at 10:22 AM Roman Gushchin
<roman.gushchin@xxxxxxxxx> wrote:
>
[...]
> > >     struct mem_cgroup *memcg;
> > > @@ -3008,19 +3054,26 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
> > >
> > >     if (in_task()) {
> > >             memcg = current->active_memcg;
> > > +           if (unlikely(memcg))
> > > +                   goto from_memcg;
> > >
> > > -           /* Memcg to charge can't be determined. */
> > > -           if (likely(!memcg) && (!current->mm || (current->flags & PF_KTHREAD)))
> >
> > The checks for current->mm and PF_KTHREAD seem to be gone completely after
> > the patch, was that intended and why?
>
> There is no need for those anymore because it's as cheap or cheaper
> to check task->objcg for being NULL. Those were primarily used to rule out
> kernel threads allocations early.
>

I have the same understanding but please correct my suspicions here.
We can echo the kernel thread's pid to cgroup.procs which have
PF_NO_SETAFFINITY and thus this will cause the lower bit of the kernel
thread's task->objcg to be set. Please correct me if I am missing
something.