linux-kernel - Re: [PATCH] mm, compaction: Indicate when compaction is manually triggered by sysctl

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Date:   Fri, 8 May 2020 11:31:12 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     "Guilherme G. Piccoli" <kernel@...ccoli.net>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Gavin Guo <gavin.guo@...onical.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH] mm, compaction: Indicate when compaction is manually
 triggered by sysctl

On Thu, 7 May 2020, Guilherme G. Piccoli wrote:

> Well...you can think that the problem we are trying to solve was more
> like...admin forgot if they triggered or not the compaction hehe
> So, counting on the user to keep track of it is what I'd like to
> avoid. And thinking about drop_caches (that have an indication when
> triggered) makes me think this indeed does make sense for compaction
> too.
> Cheers,
> 

It doesn't make sense because it's only being done here for the entire 
system, there are also per-node sysfs triggers so you could do something 
like iterate over the nodemask of all nodes with memory and trigger 
compaction manually and then nothing is emitted to the kernel log.

There is new statsfs support that Red Hat is proposing that can be used 
for things like this.  It currently only supports KVM statistics but 
adding MM statistics is something that would be a natural extension and 
avoids polluting both the kernel log and /proc/vmstat.