linux-kernel - Re: [PATCH 3/3] mm/sched: memdelay: memory health interface for systems and workloads

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Message-ID: <20170727155616.GA23665@cmpxchg.org>
Date:   Thu, 27 Jul 2017 11:56:16 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 3/3] mm/sched: memdelay: memory health interface for
 systems and workloads

On Thu, Jul 27, 2017 at 11:30:10AM -0400, Johannes Weiner wrote:
> +	/*
> +	 * The domain is somewhat delayed when a number of tasks are
> +	 * delayed but there are still others running the workload.
> +	 *
> +	 * The domain is fully delayed when all non-idle tasks on the
> +	 * CPU are delayed, or when a delayed task is actively running
> +	 * and preventing productive tasks from making headway.
> +	 *
> +	 * The state times then add up over all CPUs in the domain: if
> +	 * the domain is fully blocked on one CPU and there is another
> +	 * one running the workload, the domain is considered fully
> +	 * blocked 50% of the time.
> +	 */
> +	if (!mdc->tasks[MTS_DELAYED_ACTIVE] && !mdc->tasks[MTS_DELAYED])
> +		state = MDS_NONE;
> +	else if (mdc->tasks[MTS_WORKING])
> +		state = MDS_SOME;
> +	else
> +		state = MDS_FULL;

Just a headsup, if you're wondering why the distinction between
delayed and delayed_active: I used to track iowait separately from
working, and in a brainfart oversimplified this part right here. It
should really be:

	if (delayed_active && !iowait)
		state = full
	else if (delayed)
		state = (working || iowait) ? some : full
	else
		state = none

I'm going to re-add separate iowait tracking in v2 and fix this, but
since this patch is already big and spans two major subsystems, I
wanted to run the overall design and idea by you first before doing
more polishing on this.