linux-kernel - Re: [PATCH 1/2] mm/damon/core: add a tracepoint for damos apply target regions

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Message-ID: <20230911165144.5002a0ac@gandalf.local.home>
Date:   Mon, 11 Sep 2023 16:51:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/damon/core: add a tracepoint for damos apply
 target regions

On Mon, 11 Sep 2023 20:36:42 +0000
SeongJae Park <sj@...nel.org> wrote:

> > Then tracing is fully enabled here, and now we enter:
> > 
> >  	if (trace_damos_before_apply_enabled()) {
> > 		trace_damos_before_apply(cidx, sidx, tidx, r,
> >  				damon_nr_regions(t));
> >  	}
> > 
> > Now the trace event is hit with sidx and tidx zero when they should not be.
> > This could confuse you when looking at the report.  
> 
> Thank you so much for enlightening me with this kind explanation, Steve!  And
> this all make sense.  I will follow your suggestion in the next spin.
> 
> > 
> > What I suggested was to initialize sidx to zero,  
> 
> Nit.  Initialize to not zero but -1, right?

Yeah, but I was also thinking of the reset of it too :-p

	sidx = -1;

	if (trace_damos_before_apply_enabled()) {
		sidx = 0;

-- Steve


> 
> > set it in the first trace_*_enabled() check, and ignore calling the
> > tracepoint if it's not >= 0.
> >