From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751823Ab1HRElI (ORCPT ); Thu, 18 Aug 2011 00:41:08 -0400 Received: from mga03.intel.com ([143.182.124.21]:28959 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750706Ab1HRElF (ORCPT ); Thu, 18 Aug 2011 00:41:05 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.68,243,1312182000"; d="scan'208";a="39683080" Date: Thu, 18 Aug 2011 12:41:01 +0800 From: Wu Fengguang To: Jan Kara Cc: "linux-fsdevel@vger.kernel.org" , Peter Zijlstra , Andrew Morton , Christoph Hellwig , Dave Chinner , Greg Thelen , Minchan Kim , Vivek Goyal , Andrea Righi , linux-mm , LKML Subject: Re: [PATCH 2/5] writeback: dirty position control Message-ID: <20110818044101.GA32326@localhost> References: <20110816022006.348714319@intel.com> <20110816022328.811348370@intel.com> <20110816194112.GA25517@quack.suse.cz> <20110817132347.GA6628@localhost> <20110817202414.GK9959@quack.suse.cz> <20110818041801.GA22662@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110818041801.GA22662@localhost> 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 Hi Jan, > > > > What if x_intercept > bdi_thresh? Since 8*bdi->avg_write_bandwidth is > > > > easily 500 MB, that happens quite often I imagine? > > > > > > That's fine because I no longer target "bdi_thresh" as some limiting > > > factor as the global "thresh". Due to it being unstable in small > > > memory JBOD systems, which is the big and unique problem in JBOD. > > I see. Given the control mechanism below, I think we can try this idea > > and see whether it makes problems in practice or not. But the fact that > > bdi_thresh is no longer treated as limit should be noted in a changelog - > > probably of the last patch (although that is already too long for my taste > > so I'll look into how we could make it shorter so that average developer > > has enough patience to read it ;). > > Good point. I'll make it a comment in the last patch. Just added this comment: + /* + * bdi_thresh is not treated as some limiting factor as + * dirty_thresh, due to reasons + * - in JBOD setup, bdi_thresh can fluctuate a lot + * - in a system with HDD and USB key, the USB key may somehow + * go into state (bdi_dirty >> bdi_thresh) either because + * bdi_dirty starts high, or because bdi_thresh drops low. + * In this case we don't want to hard throttle the USB key + * dirtiers for 100 seconds until bdi_dirty drops under + * bdi_thresh. Instead the auxiliary bdi control line in + * bdi_position_ratio() will let the dirtier task progress + * at some rate <= (write_bw / 2) for bringing down bdi_dirty. + */ bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); Thanks, Fengguang From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wu Fengguang Subject: Re: [PATCH 2/5] writeback: dirty position control Date: Thu, 18 Aug 2011 12:41:01 +0800 Message-ID: <20110818044101.GA32326@localhost> References: <20110816022006.348714319@intel.com> <20110816022328.811348370@intel.com> <20110816194112.GA25517@quack.suse.cz> <20110817132347.GA6628@localhost> <20110817202414.GK9959@quack.suse.cz> <20110818041801.GA22662@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "linux-fsdevel@vger.kernel.org" , Peter Zijlstra , Andrew Morton , Christoph Hellwig , Dave Chinner , Greg Thelen , Minchan Kim , Vivek Goyal , Andrea Righi , linux-mm , LKML To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <20110818041801.GA22662@localhost> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org Hi Jan, > > > > What if x_intercept > bdi_thresh? Since 8*bdi->avg_write_bandwidth is > > > > easily 500 MB, that happens quite often I imagine? > > > > > > That's fine because I no longer target "bdi_thresh" as some limiting > > > factor as the global "thresh". Due to it being unstable in small > > > memory JBOD systems, which is the big and unique problem in JBOD. > > I see. Given the control mechanism below, I think we can try this idea > > and see whether it makes problems in practice or not. But the fact that > > bdi_thresh is no longer treated as limit should be noted in a changelog - > > probably of the last patch (although that is already too long for my taste > > so I'll look into how we could make it shorter so that average developer > > has enough patience to read it ;). > > Good point. I'll make it a comment in the last patch. Just added this comment: + /* + * bdi_thresh is not treated as some limiting factor as + * dirty_thresh, due to reasons + * - in JBOD setup, bdi_thresh can fluctuate a lot + * - in a system with HDD and USB key, the USB key may somehow + * go into state (bdi_dirty >> bdi_thresh) either because + * bdi_dirty starts high, or because bdi_thresh drops low. + * In this case we don't want to hard throttle the USB key + * dirtiers for 100 seconds until bdi_dirty drops under + * bdi_thresh. Instead the auxiliary bdi control line in + * bdi_position_ratio() will let the dirtier task progress + * at some rate <= (write_bw / 2) for bringing down bdi_dirty. + */ bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh); Thanks, Fengguang -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org