Hi Steven,
On Mon, 11 Sep 2023 14:19:55 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Mon, 11 Sep 2023 04:59:07 +0000
> SeongJae Park <sj@xxxxxxxxxx> wrote:
>
> > --- a/mm/damon/core.c
> > +++ b/mm/damon/core.c
> > @@ -950,6 +950,28 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
> > struct timespec64 begin, end;
> > unsigned long sz_applied = 0;
> > int err = 0;
> > + /*
> > + * We plan to support multiple context per kdamond, as DAMON sysfs
> > + * implies with 'nr_contexts' file. Nevertheless, only single context
> > + * per kdamond is supported for now. So, we can simply use '0' context
> > + * index here.
> > + */
> > + unsigned int cidx = 0;
> > + struct damos *siter; /* schemes iterator */
> > + unsigned int sidx = 0;
> > + struct damon_target *titer; /* targets iterator */
> > + unsigned int tidx = 0;
> > +
>
> If this loop is only for passing sidx and tidx to the trace point,
You're correct.
> you can add around it:
>
> if (trace_damos_before_apply_enabled()) {
>
> > + damon_for_each_scheme(siter, c) {
> > + if (siter == s)
> > + break;
> > + sidx++;
> > + }
> > + damon_for_each_target(titer, c) {
> > + if (titer == t)
> > + break;
> > + tidx++;
> > + }
>
> }
>
>
> And then this loop will only be done if that trace event is enabled.
Today I learned yet another great feature of the tracing framework. Thank you
Steven, I will add that to the next spin of this patchset!
>
> To prevent races, you may also want to add a third parameter, or initialize
> them to -1:
>
> sidx = -1;
>
> if (trace_damo_before_apply_enabled()) {
> sidx = 0;
> [..]
> }
>
> And you can change the TRACE_EVENT() TO TRACE_EVENT_CONDITION():
>
> TRACE_EVENT_CONDITION(damos_before_apply,
>
> TP_PROTO(...),
>
> TP_ARGS(...),
>
> TP_CONDITION(sidx >= 0),
>
> and the trace event will not be called if sidx is less than zero.
>
> Also, this if statement is only done when the trace event is enabled, so
> it's equivalent to:
>
> if (trace_damos_before_apply_enabled()) {
> if (sdx >= 0)
> trace_damos_before_apply(cidx, sidx, tidx, r,
> damon_nr_regions(t));
> }
Again, thank you very much for letting me know this awesome feature. However,
sidx is supposed to be always >=0 here, since kdamond is running in single
thread and hence no race is expected. If it exists, it's a bug. So, I
wouldn't make this change. Appreciate again for letting me know this very
useful feature, and please let me know if I'm missing something, though!
Thanks,
SJ
>
> -- Steve
>
>
>
> >
> > if (c->ops.apply_scheme) {
> > if (quota->esz && quota->charged_sz + sz > quota->esz) {
> > @@ -964,8 +986,11 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
> > ktime_get_coarse_ts64(&begin);
> > if (c->callback.before_damos_apply)
> > err = c->callback.before_damos_apply(c, t, r, s);
> > - if (!err)
> > + if (!err) {
> > + trace_damos_before_apply(cidx, sidx, tidx, r,
> > + damon_nr_regions(t));
> > sz_applied = c->ops.apply_scheme(c, t, r, s);
> > + }
> > ktime_get_coarse_ts64(&end);
> > quota->total_charged_ns += timespec64_to_ns(&end) -
> > timespec64_to_ns(&begin);
> > --
>
