Re: [Ksummit-discuss] [TECH TOPIC] Memory thrashing, was Re: Self nomination

[Rik van Riel <riel@redhat.com>]

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On Fri, 2016-07-29 at 09:26 -0700, Luck, Tony wrote:
> On Fri, Jul 29, 2016 at 12:07:24PM +0100, Mel Gorman wrote:
> > On Thu, Jul 28, 2016 at 02:55:23PM -0400, Johannes Weiner wrote:
> > > On Mon, Jul 25, 2016 at 01:11:42PM -0400, Johannes Weiner wrote:
> 
> > > It might be useful to talk about
> > > metrics. Could we quantify application progress?
> 
> The most reliable way to do that would be to have an actual
> user mode program that runs, accessing some configurable number
> of pages, periodically touching some file in /proc/sys/vm to
> let the kernel know that some quantum of work had been completed.

I don't think there is a need for that.

We already keep track of how much user time and how
much system time a program uses, and how much time
it is stalled on IO.

If user time is low, a program is stalled on IO a
lot of the time, and a lot of the faults are refaults
(previously accessed memory), then we are thrashing.

If the program is not stalled on IO much, or is
accessing pages it has not previously accessed
before, it is not thrashing.

We probably have the right statistics already, unless
I am overlooking something.

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