linux-kernel - Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat

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Message-ID: <20170425193619.GA8403@amt.cnet>
Date:   Tue, 25 Apr 2017 16:36:21 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Rik van Riel <riel@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Linux RT Users <linux-rt-users@...r.kernel.org>
Subject: Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and vmstat_worker
 configuration

On Tue, Apr 25, 2017 at 03:29:06PM -0400, Rik van Riel wrote:
> On Tue, 2017-04-25 at 10:57 -0300, Marcelo Tosatti wrote:
> > The per-CPU vmstat worker is a problem on -RT workloads (because
> > ideally the CPU is entirely reserved for the -RT app, without
> > interference). The worker transfers accumulated per-CPU 
> > vmstat counters to global counters.
> > 
> > To resolve the problem, create two tunables:
> > 
> > * Userspace configurable per-CPU vmstat threshold: by default the 
> > VM code calculates the size of the per-CPU vmstat arrays. This 
> > tunable allows userspace to configure the values.
> > 
> > * Userspace configurable per-CPU vmstat worker: allow disabling
> > the per-CPU vmstat worker.
> > 
> > The patch below contains documentation which describes the tunables
> > in more detail.
> 
> The documentation says what the tunables do, but
> not how you should set them in different scenarios,
> or why.
> 
> That could be a little more helpful to sysadmins.

OK i'll update the document to be more verbose.