From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f53.google.com (mail-pa0-f53.google.com [209.85.220.53]) by kanga.kvack.org (Postfix) with ESMTP id 7C37C6B0038 for ; Mon, 23 Nov 2015 21:16:21 -0500 (EST) Received: by padhx2 with SMTP id hx2so4436108pad.1 for ; Mon, 23 Nov 2015 18:16:21 -0800 (PST) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTPS id q88si23585028pfa.36.2015.11.23.18.16.19 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 23 Nov 2015 18:16:20 -0800 (PST) Date: Tue, 24 Nov 2015 10:45:28 +0900 From: Joonsoo Kim Subject: Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation Message-ID: <20151124014527.GA32335@js1304-P5Q-DELUXE> References: <1447053784-27811-1-git-send-email-iamjoonsoo.kim@lge.com> <1447053784-27811-2-git-send-email-iamjoonsoo.kim@lge.com> <564C9A86.1090906@suse.cz> <20151120063325.GB13061@js1304-P5Q-DELUXE> <20151120114225.7efeeafe@grimm.local.home> <20151123082805.GB29397@js1304-P5Q-DELUXE> <20151123092604.7ec1397d@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151123092604.7ec1397d@gandalf.local.home> Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt Cc: Vlastimil Babka , Andrew Morton , Michal Nazarewicz , Minchan Kim , Mel Gorman , "Kirill A. Shutemov" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org On Mon, Nov 23, 2015 at 09:26:04AM -0500, Steven Rostedt wrote: > On Mon, 23 Nov 2015 17:28:05 +0900 > Joonsoo Kim 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 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org