On Mon, Nov 23, 2015 at 09:26:04AM -0500, Steven Rostedt wrote:
> On Mon, 23 Nov 2015 17:28:05 +0900
> Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
>
> > On Fri, Nov 20, 2015 at 11:42:25AM -0500, Steven Rostedt wrote:
> > > On Fri, 20 Nov 2015 15:33:25 +0900
> > > Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> > >
> > >
> > > > Steven, is it possible to add tracepoint to inlined fucntion such as
> > > > get_page() in include/linux/mm.h?
> > >
> > > I highly recommend against it. The tracepoint code adds a bit of bloat,
> > > and if you inline it, you add that bloat to every use case. Also, it
> >
> > Is it worse than adding function call to my own stub function into
> > inlined function such as get_page(). I implemented it as following.
> >
> > get_page()
> > {
> > atomic_inc()
> > stub_get_page()
> > }
> >
> > stub_get_page() in foo.c
> > {
> > trace_page_ref_get_page()
> > }
>
> Now you just slowed down the fast path. But what you could do is:
>
> get_page()
> {
> atomic_inc();
> if (trace_page_ref_get_page_enabled())
> stub_get_page();
> }
>
> Now that "trace_page_ref_get_page_enabled()" will turn into:
>
> if (static_key_false(&__tracepoint_page_ref_get_page.key)) {
>
> which is a jump label (nop when disabled, a jmp when enabled). That's
> less bloat but doesn't solve the include problem. You still need to add
> the include of that will cause havoc with other tracepoints.
Yes, It also has a include dependency problem so I can't use
trace_page_ref_get_page_enabled() in mm.h. BTW, I tested following
implementation and it works fine.
extern struct tracepoint __tracepoint_page_ref_get_page;
get_page()
{
atomic_inc()
if (static_key_false(&__tracepoint_page_ref_get_page.key))
stub_get_page()
}
This would not slow down fast path although it can't prevent bloat.
I know that it isn't good code practice, but, this page reference
handling functions have complex include dependency so I'm not sure
I can solve it completely. For this special case, can I use
this raw data structure?
Thanks.
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