Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932247AbbLCEQG (ORCPT ); Wed, 2 Dec 2015 23:16:06 -0500 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:44647 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932180AbbLCEQE (ORCPT ); Wed, 2 Dec 2015 23:16:04 -0500 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Thu, 3 Dec 2015 13:16:58 +0900 From: Joonsoo Kim 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 Subject: Re: [PATCH 2/2] mm/page_ref: add tracepoint to track down page reference manipulation Message-ID: <20151203041657.GB1495@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> <20151124014527.GA32335@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151124014527.GA32335@js1304-P5Q-DELUXE> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2558 Lines: 76 On Tue, Nov 24, 2015 at 10:45:28AM +0900, Joonsoo Kim wrote: > 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? > Steven, any comment? Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/