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Date: Tue, 24 Nov 2015 10:45:28 +0900 From: Joonsoo Kim <iamjoonsoo.kim@....com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Vlastimil Babka <vbabka@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>, Michal Nazarewicz <mina86@...a86.com>, Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org Subject: Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation 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@....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@....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 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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