Re: Re: [PATCH v14 09/15] mm/damon: Add tracepoints

[SeongJae Park <sjpark@amazon.com>]

On Tue, 2 Jun 2020 11:35:36 -0400 Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 2 Jun 2020 15:12:49 +0200
> SeongJae Park <sjpark@amazon.com> wrote:
> 
> > From: SeongJae Park <sjpark@amazon.de>
> > 
> > This commit adds a tracepoint for DAMON.  It traces the monitoring
> > results of each region for each aggregation interval.  Using this, DAMON
> > will be easily integrated with any tracepoints supporting tools such as
> > perf.
> > 
> > Signed-off-by: SeongJae Park <sjpark@amazon.de>
> > Reviewed-by: Leonard Foerster <foersleo@amazon.de>
> > ---
> >  include/trace/events/damon.h | 43 ++++++++++++++++++++++++++++++++++++
> >  mm/damon.c                   |  5 +++++
> >  2 files changed, 48 insertions(+)
> >  create mode 100644 include/trace/events/damon.h
> > 
> > diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
> > new file mode 100644
> > index 000000000000..22236642d366
> > --- /dev/null
> > +++ b/include/trace/events/damon.h
> > @@ -0,0 +1,43 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM damon
> > +
> > +#if !defined(_TRACE_DAMON_H) || defined(TRACE_HEADER_MULTI_READ)
> > +#define _TRACE_DAMON_H
> > +
> > +#include <linux/types.h>
> > +#include <linux/tracepoint.h>
> > +
> > +TRACE_EVENT(damon_aggregated,
> > +
> > +	TP_PROTO(int pid, unsigned int nr_regions,
> > +		unsigned long vm_start, unsigned long vm_end,
> > +		unsigned int nr_accesses),
> > +
> > +	TP_ARGS(pid, nr_regions, vm_start, vm_end, nr_accesses),
> > +
> > +	TP_STRUCT__entry(
> > +		__field(int, pid)
> > +		__field(unsigned int, nr_regions)
> > +		__field(unsigned long, vm_start)
> > +		__field(unsigned long, vm_end)
> > +		__field(unsigned int, nr_accesses)
> > +	),
> > +
> > +	TP_fast_assign(
> > +		__entry->pid = pid;
> > +		__entry->nr_regions = nr_regions;
> > +		__entry->vm_start = vm_start;
> > +		__entry->vm_end = vm_end;
> > +		__entry->nr_accesses = nr_accesses;
> > +	),
> > +
> > +	TP_printk("pid=%d nr_regions=%u %lu-%lu: %u", __entry->pid,
> > +			__entry->nr_regions, __entry->vm_start,
> > +			__entry->vm_end, __entry->nr_accesses)
> > +);
> > +
> > +#endif /* _TRACE_DAMON_H */
> > +
> > +/* This part must be outside protection */
> > +#include <trace/define_trace.h>
> > diff --git a/mm/damon.c b/mm/damon.c
> > index 6b0b8f21a6c6..af6f395fe06c 100644
> > --- a/mm/damon.c
> > +++ b/mm/damon.c
> > @@ -9,6 +9,8 @@
> >  
> >  #define pr_fmt(fmt) "damon: " fmt
> >  
> > +#define CREATE_TRACE_POINTS
> > +
> >  #include <linux/damon.h>
> >  #include <linux/debugfs.h>
> >  #include <linux/delay.h>
> > @@ -20,6 +22,7 @@
> >  #include <linux/sched/mm.h>
> >  #include <linux/sched/task.h>
> >  #include <linux/slab.h>
> > +#include <trace/events/damon.h>
> >  
> >  /* Minimal region size.  Every damon_region is aligned by this. */
> >  #define MIN_REGION PAGE_SIZE
> > @@ -650,6 +653,8 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
> >  			damon_write_rbuf(c, &r->vm_end, sizeof(r->vm_end));
> >  			damon_write_rbuf(c, &r->nr_accesses,
> >  					sizeof(r->nr_accesses));
> > +			trace_damon_aggregated(t->pid, nr,
> > +					r->vm_start, r->vm_end, r->nr_accesses);
> 
> For a little better code, what about passing in t and r directly, and then
> having the TP_fast_assign just do the dereferencing there?
> 
> 	__entry->pid = t->pid;
> 	__entry->vm_start = r->vm_start;
> 	__entry->vm_end = r->vm_end;
> 	__entry->nr_accesses = r->nr_accesses;
> 
> It will produce better code at the trace point call (which is the important
> part) and make the trace event a bit more flexible in the future, without
> having to modify the call site.

Good point, I will do so in the next spin!


Thanks,
SeongJae Park

> 
> -- Steve
> 
> 
> >  			r->nr_accesses = 0;
> >  		}
> >  	}