From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753867Ab0G1CEM (ORCPT ); Tue, 27 Jul 2010 22:04:12 -0400 Received: from mga01.intel.com ([192.55.52.88]:21787 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752633Ab0G1CEK (ORCPT ); Tue, 27 Jul 2010 22:04:10 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.55,271,1278313200"; d="scan'208";a="822341957" Date: Wed, 28 Jul 2010 10:04:07 +0800 From: Wu Fengguang To: Jan Kara Cc: Andrew Morton , Christoph Hellwig , Peter Zijlstra , Richard Kennedy , Dave Chinner , "linux-fsdevel@vger.kernel.org" , Linux Memory Management List , LKML Subject: Re: [PATCH 2/6] writeback: reduce calls to global_page_state in balance_dirty_pages() Message-ID: <20100728020407.GA9819@localhost> References: <20100711020656.340075560@intel.com> <20100711021748.735126772@intel.com> <20100726151946.GH3280@quack.suse.cz> <20100727035941.GA15007@localhost> <20100727091220.GD3358@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100727091220.GD3358@quack.suse.cz> 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 > > The global threshold check is added in place of clip_bdi_dirty_limit() > > for safety and not intended as a behavior change. If ever leading to > > big behavior change and regression, that it would be indicating some > > too permissive per-bdi threshold calculation. > > > > Did you see the global dirty threshold get exceeded when writing to 2+ > > devices? Occasional small exceeding should be OK though. I tried the > > following debug patch and see no warnings when doing two concurrent cp > > over local disk and NFS. > Oops, sorry. I've misread the code. You're right. There shouldn't be a big > change in the behavior. It does indicate a missing point in the changelog. The paragraph is updated to: We now set and clear dirty_exceeded not only based on bdi dirty limits, but also on the global dirty limit. The global limit check is added in place of clip_bdi_dirty_limit() for safety and not intended as a behavior change. The bdi limits should be tight enough to keep all dirty pages under the global limit at most time; occasional small exceeding should be OK though. The change makes the logic more obvious: the global limit is the ultimate goal and shall be always imposed. Thanks, Fengguang