Re: [patch 026/158] mm: emit tracepoint when RSS changes

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 2 Dec 2019 16:13:45 -0500
Joel Fernandes <joel@joelfernandes.org> wrote:

> On Mon, Dec 02, 2019 at 12:14:15PM -0500, Steven Rostedt wrote:
> > On Sat, 30 Nov 2019 17:50:30 -0800
> > akpm@linux-foundation.org wrote:
> >   
> > >  /* Optimized variant when page is already known not to be PageAnon */
> > > --- a/include/trace/events/kmem.h~mm-emit-tracepoint-when-rss-changes
> > > +++ a/include/trace/events/kmem.h
> > > @@ -316,6 +316,27 @@ TRACE_EVENT(mm_page_alloc_extfrag,
> > >  		__entry->change_ownership)
> > >  );
> > >  
> > > +TRACE_EVENT(rss_stat,
> > > +
> > > +	TP_PROTO(int member,
> > > +		long count),
> > > +
> > > +	TP_ARGS(member, count),
> > > +
> > > +	TP_STRUCT__entry(
> > > +		__field(int, member)
> > > +		__field(long, size)
> > > +	),
> > > +
> > > +	TP_fast_assign(
> > > +		__entry->member = member;
> > > +		__entry->size = (count << PAGE_SHIFT);  
> > 
> > It's best to put all calculations (including shifts) in the print part,
> > as that's the slow path. The TP_fast_assign() is done when the trace
> > point is triggered (during the execution of the code). It's best to
> > keep this in the slow path (TP_printk).
> > 
> > 		__entry->count = count;
> >   
> > > +	),
> > > +
> > > +	TP_printk("member=%d size=%ldB",
> > > +		__entry->member,
> > > +		__entry->size)  
> > 
> > 		__entry->count << PAGE_SHIFT)  
> 
> Ah. Android users now use a tool called perfetto which gather raw trace
> (binary format). So such shifting will have to be done by userspace then if
> we did it this way. And I'm afraid this patch has been in circulation for
> quite some time now that may cause major pains in changing userspace tooling
> now :-\
> 

I've been trying to get libtraceevent into a standard library, and
it's been ready to go. Can your tool please use that. It can handle this
without issue. Just feed it the format file (that's exported to
user space via the tracefs file system).

-- Steve