Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752832Ab0HTInM (ORCPT ); Fri, 20 Aug 2010 04:43:12 -0400 Received: from mga01.intel.com ([192.55.52.88]:20535 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752235Ab0HTInK (ORCPT ); Fri, 20 Aug 2010 04:43:10 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.56,238,1280732400"; d="scan'208";a="598535188" Date: Fri, 20 Aug 2010 16:43:04 +0800 From: Wu Fengguang To: Michael Rubin Cc: "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "jack@suse.cz" , "riel@redhat.com" , "akpm@linux-foundation.org" , "david@fromorbit.com" , "npiggin@suse.de" , "hch@lst.de" , "axboe@kernel.dk" Subject: Re: [PATCH 2/3] writeback: Adding pages_dirtied and pages_entered_writeback Message-ID: <20100820084304.GA6051@localhost> References: <1282251447-16937-1-git-send-email-mrubin@google.com> <1282251447-16937-3-git-send-email-mrubin@google.com> <20100820025111.GB5502@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2725 Lines: 57 On Fri, Aug 20, 2010 at 04:16:09PM +0800, Michael Rubin wrote: > On Thu, Aug 19, 2010 at 7:51 PM, Wu Fengguang wrote: > > As Rik said, /proc/sys is not a suitable place. > > OK I'm convinced. > > > Frankly speaking I've worked on writeback for years and never felt > > the need to add these counters. What I often do is: > > > > $ vmmon -d 1 nr_writeback nr_dirty nr_unstable > > > >     nr_writeback         nr_dirty      nr_unstable > >            68738                0            39568 > >            66051                0            42255 > >            63406                0            44900 > >            60643                0            47663 > >            57954                0            50352 > >            55264                0            53042 > >            52592                0            55715 > >            49922                0            58385 > > That is what I get when copying /dev/zero to NFS. > > > > I'm very interested in Google's use case for this patch, and why > > the simple /proc/vmstat based vmmon tool is not enough. > > So as I understand it from looking at the code vmmon is sampling > nr_writeback, nr_dirty which are exported versions of > global_page_state for NR_FILE_DIRTY and NR_WRITEBACK. These states are > a snapshot of the state of the kernel's pages. Namely how many dpages > ar ein writeback or dirty at the moment vmmon's acquire routine is > called. > > vmmon is sampling /proc/vstat and then displaying the difference from > the last time they sampled. If I am misunderstanding let me know. Maybe Andrew's vmmon does that. My vmmon always display the raw values :) It could be improved to do raw values for nr_dirty and differences for pgpgin by default. > This is good for the state of the system but as we compare > application, mm and io performance over long periods of time we are > interested in the surges and fluctuations of the rates of the > producing and consuming of dirty pages also. It can help isolate where > the problem is and also to compare performance between kernels and/or > applications. Yeah the accumulated dirty and writeback page counts could be useful. For example, for inspecting the dirty and writeback speed over time. That's not possible for nr_dirty/nr_writeback. Thanks, Fengguang -- 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/