linux-kernel - Re: [PATCH] tracing, memcg, vmscan: Hide trace events when not in use

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Message-ID: <20171013102848.34dec4a7@gandalf.local.home>
Date:   Fri, 13 Oct 2017 10:28:48 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Balbir Singh <balbir@...ux.vnet.ibm.com>,
        KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] tracing, memcg, vmscan: Hide trace events when not in
 use

On Fri, 13 Oct 2017 08:38:26 +0200
Michal Hocko <mhocko@...nel.org> wrote:

> I do not understand the ftrace machinery 

Not many do :-/

> and I have to admit I was under
> impression that nothing really gets defined if the code using them
> doesn't exist but if this is not the case then this patch makes sense to
> me

Sometimes events are created by kernel proper that are used by modules,
or created by modules to be used by other modules (kvm does this with
kvm_intel and kvm_amd). Unfortunately, for these cases they need to
stay. Or later, I plan on moving them to where they are used, because
they have the same issue (wasting memory).

> 
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>  
> 
> Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

-- Steve