Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752034AbbLJC6l (ORCPT ); Wed, 9 Dec 2015 21:58:41 -0500 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:37978 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751720AbbLJC6j (ORCPT ); Wed, 9 Dec 2015 21:58:39 -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, 10 Dec 2015 11:50:15 +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: <20151210025015.GA17967@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> <20151203041657.GB1495@js1304-P5Q-DELUXE> <20151209150154.31c142b9@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151209150154.31c142b9@gandalf.local.home> 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: 4751 Lines: 119 On Wed, Dec 09, 2015 at 03:01:54PM -0500, Steven Rostedt wrote: > On Thu, 3 Dec 2015 13:16:58 +0900 > Joonsoo Kim wrote: > > > 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? > > Sorry for the later reply, I was going to reply but then got called off > to do something else, and then forgot about this message :-/ No problem. :) > > I wanted you to look at what Andi has done here: > > http://lkml.kernel.org/r/1449018060-1742-2-git-send-email-andi@firstfloor.org > > and here > > http://lkml.kernel.org/r/1449018060-1742-3-git-send-email-andi@firstfloor.org Wow...They look like what I'm looking for. Nice! Thanks for the pointer! I have one more question about trace-cmd. 'trace-cmd report' shows time-sorted output even stack trace. See following example. trace-cmd-6338 [003] 54.046508: page_ref_mod: ... trace-cmd-6583 [007] 54.046509: page_ref_mod: ... trace-cmd-6338 [003] 54.046515: kernel_stack: => do_wp_page (ffffffff811a0c6f) => handle_mm_fault (ffffffff811a34e2) => __do_page_fault (ffffffff810632da) => trace_do_page_fault (ffffffff81063633) => do_async_page_fault (ffffffff8105c3ea) => async_page_fault (ffffffff817733f8) trace-cmd-6583 [007] 54.046515: kernel_stack: => do_wp_page (ffffffff811a0c6f) => handle_mm_fault (ffffffff811a34e2) ... Output of cpu 3, 7 are mixed and it's not easy to analyze it. I think that it'd be better not to sort stack trace. How do you think about it? Could you fix it, please? 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/