2023-09-12 05:17:57

by SeongJae Park

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

On Mon, 11 Sep 2023 16:51:44 -0400 Steven Rostedt <[email protected]> wrote:

> On Mon, 11 Sep 2023 20:36:42 +0000
> SeongJae Park <[email protected]> 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;

Thank you for clarifying, Steve :)

Nevertheless, since the variable is unsigned int, I would need to use UINT_MAX
instead. To make the code easier to understand, I'd prefer to add a third
parameter, as you suggested as another option at the original reply, like
below:

--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -997,6 +997,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
unsigned int sidx = 0;
struct damon_target *titer; /* targets iterator */
unsigned int tidx = 0;
+ bool do_trace = false;

/* get indices for trace_damos_before_apply() */
if (trace_damos_before_apply_enabled()) {
@@ -1010,6 +1011,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
break;
tidx++;
}
+ do_trace = true;
}

if (c->ops.apply_scheme) {
@@ -1036,7 +1038,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
err = c->callback.before_damos_apply(c, t, r, s);
if (!err) {
trace_damos_before_apply(cidx, sidx, tidx, r,
- damon_nr_regions(t));
+ damon_nr_regions(t), do_trace);
sz_applied = c->ops.apply_scheme(c, t, r, s);
}
ktime_get_coarse_ts64(&end);


Thanks,
SJ

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

2023-09-12 06:20:25

by Steven Rostedt

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

On Tue, 12 Sep 2023 01:43:08 +0000
SeongJae Park <[email protected]> wrote:

> Nevertheless, since the variable is unsigned int, I would need to use UINT_MAX
> instead. To make the code easier to understand, I'd prefer to add a third
> parameter, as you suggested as another option at the original reply, like
> below:

That works too.

-- Steve