From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752349AbcL3JhA (ORCPT ); Fri, 30 Dec 2016 04:37:00 -0500 Received: from mx2.suse.de ([195.135.220.15]:44775 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751521AbcL3Jg6 (ORCPT ); Fri, 30 Dec 2016 04:36:58 -0500 Date: Fri, 30 Dec 2016 10:36:55 +0100 From: Michal Hocko To: Mel Gorman Cc: linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Vlastimil Babka , Rik van Riel , LKML Subject: Re: [PATCH 0/7] vm, vmscan: enahance vmscan tracepoints Message-ID: <20161230093654.GC13301@dhcp22.suse.cz> References: <20161228153032.10821-1-mhocko@kernel.org> <20161230091117.nkxn3bnhle3bofhw@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161230091117.nkxn3bnhle3bofhw@suse.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 30-12-16 09:11:17, Mel Gorman wrote: > On Wed, Dec 28, 2016 at 04:30:25PM +0100, Michal Hocko wrote: > > Hi, > > while debugging [1] I've realized that there is some room for > > improvements in the tracepoints set we offer currently. I had hard times > > to make any conclusion from the existing ones. The resulting problem > > turned out to be active list aging [2] and we are missing at least two > > tracepoints to debug such a problem. > > > > Some existing tracepoints could export more information to see _why_ the > > reclaim progress cannot be made not only _how much_ we could reclaim. > > The later could be seen quite reasonably from the vmstat counters > > already. It can be argued that we are showing too many implementation > > details in those tracepoints but I consider them way too lowlevel > > already to be usable by any kernel independent userspace. I would be > > _really_ surprised if anything but debugging tools have used them. > > > > Any feedback is highly appreciated. > > > > There is some minor overhead introduced in some paths regardless of > whether the tracepoints are active or not but I suspect it's negligible > in the context of the overhead of reclaim in general so; I will work on improving some of them. E.g. I've dropped the change to free_hot_cold_page_list because that is indeed a hot path but other than that there shouldn't be any even medium hot path which should see any overhead I can see. If you are aware of any, please let me know and I will think about how to improve it. > Acked-by: Mel Gorman Thanks! -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 2D6B16B0038 for ; Fri, 30 Dec 2016 04:36:59 -0500 (EST) Received: by mail-wm0-f71.google.com with SMTP id c85so34908213wmi.6 for ; Fri, 30 Dec 2016 01:36:59 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id yr4si61542378wjc.210.2016.12.30.01.36.57 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 30 Dec 2016 01:36:57 -0800 (PST) Date: Fri, 30 Dec 2016 10:36:55 +0100 From: Michal Hocko Subject: Re: [PATCH 0/7] vm, vmscan: enahance vmscan tracepoints Message-ID: <20161230093654.GC13301@dhcp22.suse.cz> References: <20161228153032.10821-1-mhocko@kernel.org> <20161230091117.nkxn3bnhle3bofhw@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161230091117.nkxn3bnhle3bofhw@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Vlastimil Babka , Rik van Riel , LKML On Fri 30-12-16 09:11:17, Mel Gorman wrote: > On Wed, Dec 28, 2016 at 04:30:25PM +0100, Michal Hocko wrote: > > Hi, > > while debugging [1] I've realized that there is some room for > > improvements in the tracepoints set we offer currently. I had hard times > > to make any conclusion from the existing ones. The resulting problem > > turned out to be active list aging [2] and we are missing at least two > > tracepoints to debug such a problem. > > > > Some existing tracepoints could export more information to see _why_ the > > reclaim progress cannot be made not only _how much_ we could reclaim. > > The later could be seen quite reasonably from the vmstat counters > > already. It can be argued that we are showing too many implementation > > details in those tracepoints but I consider them way too lowlevel > > already to be usable by any kernel independent userspace. I would be > > _really_ surprised if anything but debugging tools have used them. > > > > Any feedback is highly appreciated. > > > > There is some minor overhead introduced in some paths regardless of > whether the tracepoints are active or not but I suspect it's negligible > in the context of the overhead of reclaim in general so; I will work on improving some of them. E.g. I've dropped the change to free_hot_cold_page_list because that is indeed a hot path but other than that there shouldn't be any even medium hot path which should see any overhead I can see. If you are aware of any, please let me know and I will think about how to improve it. > Acked-by: Mel Gorman Thanks! -- Michal Hocko SUSE Labs -- 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