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Subject: Re: [patch 2/2] MM: allow per-cpu vmstat_threshold and
 vmstat_worker configuration
From: Rik van Riel <riel@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
        Linux RT Users <linux-rt-users@vger.kernel.org>
Date: Tue, 25 Apr 2017 15:29:06 -0400
In-Reply-To: <20170425135846.203663532@redhat.com>
References: <20170425135717.375295031@redhat.com>
         <20170425135846.203663532@redhat.com>
Organization: Red Hat, Inc
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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.