linux-kernel - Re: [PATCH 09/10] psi: cgroup support

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Message-ID: <20180717154059.GB2476@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Jul 2018 17:40:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Christopher Lameter <cl@...ux.com>,
        Mike Galbraith <efault@....de>,
        Shakeel Butt <shakeelb@...gle.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 09/10] psi: cgroup support

On Thu, Jul 12, 2018 at 01:29:41PM -0400, Johannes Weiner wrote:
> +/**
> + * cgroup_move_task - move task to a different cgroup
> + * @task: the task
> + * @to: the target css_set
> + *
> + * Move task to a new cgroup and safely migrate its associated stall
> + * state between the different groups.
> + *
> + * This function acquires the task's rq lock to lock out concurrent
> + * changes to the task's scheduling state and - in case the task is
> + * running - concurrent changes to its stall state.
> + */
> +void cgroup_move_task(struct task_struct *task, struct css_set *to)
> +{
> +	unsigned int task_flags = 0;
> +	struct rq_flags rf;
> +	struct rq *rq;
> +	u64 now;
> +
> +	rq = task_rq_lock(task, &rf);
> +
> +	if (task_on_rq_queued(task)) {
> +		task_flags = TSK_RUNNING;
> +	} else if (task->in_iowait) {
> +		task_flags = TSK_IOWAIT;
> +	}
> +	if (task->flags & PF_MEMSTALL)
> +		task_flags |= TSK_MEMSTALL;
> +
> +	if (task_flags) {
> +		update_rq_clock(rq);
> +		now = rq_clock(rq);
> +		psi_task_change(task, now, task_flags, 0);
> +	}
> +
> +	/*
> +	 * Lame to do this here, but the scheduler cannot be locked
> +	 * from the outside, so we move cgroups from inside sched/.
> +	 */
> +	rcu_assign_pointer(task->cgroups, to);
> +
> +	if (task_flags)
> +		psi_task_change(task, now, 0, task_flags);
> +
> +	task_rq_unlock(rq, task, &rf);
> +}

Why is that not part of cpu_cgroup_attach() / sched_move_task() ?