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

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Message-ID: <20170801075728.GE6524@worktop.programming.kicks-ass.net>
Date:   Tue, 1 Aug 2017 09:57:28 +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>,
        Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
        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 Mon, Jul 31, 2017 at 02:41:42PM -0400, Johannes Weiner wrote:
> On Mon, Jul 31, 2017 at 10:31:11AM +0200, Peter Zijlstra wrote:

> > So could you start by describing what actual statistics we need? Because
> > as is the scheduler already does a gazillion stats and why can't re
> > repurpose some of those?
> 
> If that's possible, that would be great of course.
> 
> We want to be able to tell how many tasks in a domain (the system or a
> memory cgroup) are inside a memdelay section as opposed to how many

And you haven't even defined wth a memdelay section is yet..

> are in a "productive" state such as runnable or iowait. Then derive
> from that whether the domain as a whole is unproductive (all non-idle
> tasks memdelayed), or partially unproductive (some delayed, but CPUs
> are productive or there are iowait tasks). Then derive the percentages
> of walltime the domain spends partially or fully unproductive.
> 
> For that we need per-domain counters for
> 
> 	1) nr of tasks in memdelay sections
> 	2) nr of iowait or runnable/queued tasks that are NOT inside
> 	   memdelay sections

And I still have no clue..