From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755935Ab0BOPro (ORCPT ); Mon, 15 Feb 2010 10:47:44 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50853 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755917Ab0BOPrl (ORCPT ); Mon, 15 Feb 2010 10:47:41 -0500 Date: Mon, 15 Feb 2010 16:47:51 +0100 From: Jan Kara To: Andrew Morton Cc: Jan Kara , LKML , npiggin@suse.de, fengguang.wu@intel.com Subject: Re: [PATCH 2/3] mm: Implement writeback livelock avoidance using page tagging Message-ID: <20100215154751.GG3434@quack.suse.cz> References: <1265929584-5080-1-git-send-email-jack@suse.cz> <1265929584-5080-3-git-send-email-jack@suse.cz> <20100212113955.4c023130.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100212113955.4c023130.akpm@linux-foundation.org> 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 On Fri 12-02-10 11:39:55, Andrew Morton wrote: > On Fri, 12 Feb 2010 00:06:23 +0100 > Jan Kara wrote: > > > The idea is simple: Tag all pages that should be written back > > with a special tag (TOWRITE) in the radix tree. This can be done > > rather quickly and thus livelocks should not happen in practice. > > Then we start doing the hard work of locking pages and sending > > them to disk only for those pages that have TOWRITE tag set. > > Adding a second pass across all the pages sounds expensive? Strictly speaking it's just through the radix tree and only through branches with DIRTY_TAG set. But yes, there is some additional CPU cost. I just thought that given the total cost of submitting a page it is an acceptable increase and the simplification is worth it. Would some numbers make you happier? Any suggestion for measurements? Because I think that even for writes to tmpfs the change will be lost in the noise... Honza -- Jan Kara SUSE Labs, CR