Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO

On Mon, May 07, 2018 at 05:01:34PM -0400, Johannes Weiner wrote:

+/**
+ * psi_memstall_enter - mark the beginning of a memory stall section
+ * @flags: flags to handle nested sections
+ *
+ * Marks the calling task as being stalled due to a lack of memory,
+ * such as waiting for a refault or performing reclaim.
+ */
+void psi_memstall_enter(unsigned long *flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	*flags = current->flags & PF_MEMSTALL;
+	if (*flags)
+		return;
+	/*
+	 * PF_MEMSTALL setting & accounting needs to be atomic wrt
+	 * changes to the task's scheduling state, otherwise we can
+	 * race with CPU migration.
+	 */
+	local_irq_disable();
+	rq = this_rq();
+	raw_spin_lock(&rq->lock);
+	rq_pin_lock(rq, &rf);

Given that churn in sched.h, you seen rq_lock() and friends.

Either write this like:

	local_irq_disable();
	rq = this_rq();
	rq_lock(rq, &rf);

Or instroduce "rq = this_rq_lock_irq()", which we could also use in
do_sched_yield().

+	update_rq_clock(rq);
+
+	current->flags |= PF_MEMSTALL;
+	psi_task_change(current, rq_clock(rq), 0, TSK_MEMSTALL);
+
+	rq_unpin_lock(rq, &rf);
+	raw_spin_unlock(&rq->lock);
+	local_irq_enable();

That's called rq_unlock_irq().

+}
+
+/**
+ * psi_memstall_leave - mark the end of an memory stall section
+ * @flags: flags to handle nested memdelay sections
+ *
+ * Marks the calling task as no longer stalled due to lack of memory.
+ */
+void psi_memstall_leave(unsigned long *flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	if (*flags)
+		return;
+	/*
+	 * PF_MEMSTALL clearing & accounting needs to be atomic wrt
+	 * changes to the task's scheduling state, otherwise we could
+	 * race with CPU migration.
+	 */
+	local_irq_disable();
+	rq = this_rq();
+	raw_spin_lock(&rq->lock);
+	rq_pin_lock(rq, &rf);
+
+	update_rq_clock(rq);
+
+	current->flags &= ~PF_MEMSTALL;
+	psi_task_change(current, rq_clock(rq), TSK_MEMSTALL, 0);
+
+	rq_unpin_lock(rq, &rf);
+	raw_spin_unlock(&rq->lock);
+	local_irq_enable();
+}

Idem.