Messages in this thread | | | Date | Tue, 24 Nov 2015 10:56:04 +0900 | From | Joonsoo Kim <> | Subject | Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation |
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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@lge.com> 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@lge.com> 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 include dependency problem so I can't use trace_page_ref_get_page_enabled() in mm.h.
BTW, I try to open code trace_page_ref_get_page_enabled() in get_page() as following 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() }
I know that it's not good coding practice to use raw data structure, but, page reference management functions has complex dependency so I'm not sure I can solve it completely. For this special case, can I use it?
Thanks.
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