Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933183Ab2JSOi3 (ORCPT ); Fri, 19 Oct 2012 10:38:29 -0400 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:41709 "EHLO e06smtp13.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933018Ab2JSOiV (ORCPT ); Fri, 19 Oct 2012 10:38:21 -0400 Date: Fri, 19 Oct 2012 16:38:14 +0200 From: Martin Schwidefsky To: Hugh Dickins Cc: Jan Kara , linux-mm@kvack.org, LKML , xfs@oss.sgi.com, Mel Gorman , linux-s390@vger.kernel.org Subject: Re: [PATCH] mm: Fix XFS oops due to dirty pages without buffers on s390 Message-ID: <20121019163814.55b3590e@mschwide> In-Reply-To: References: <1349108796-32161-1-git-send-email-jack@suse.cz> <20121009101822.79bdcb65@mschwide> Organization: IBM Corporation X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit x-cbid: 12101914-2966-0000-0000-00000598A146 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1827 Lines: 46 On Tue, 9 Oct 2012 16:21:24 -0700 (PDT) Hugh Dickins wrote: > > > > I am seriously tempted to switch to pure software dirty bits by using > > page protection for writable but clean pages. The worry is the number of > > additional protection faults we would get. But as we do software dirty > > bit tracking for the most part anyway this might not be as bad as it > > used to be. > > That's exactly the same reason why tmpfs opts out of dirty tracking, fear > of unnecessary extra faults. Anomalous as s390 is here, tmpfs is being > anomalous too, and I'd be a hypocrite to push for you to make that change. I tested the waters with the software dirty bit idea. Using kernel compile as test case I got these numbers: disk backing, swdirty: 10,023,870 minor-faults 18 major-faults disk backing, hwdirty: 10,023,829 minor-faults 21 major-faults tmpfs backing, swdirty: 10,019,552 minor-faults 49 major-faults tmpfs backing, hwdirty: 10,032,909 minor-faults 81 major-faults That does not look bad at all. One test I found that shows an effect is lat_mmap from LMBench: disk backing, hwdirty: 30,894 minor-faults 0 major-faults disk backing, swdirty: 30,894 minor-faults 0 major-faults tmpfs backing, hwdirty: 22,574 minor-faults 0 major-faults tmpfs backing, swdirty: 36,652 minor-faults 0 major-faults The runtime between the hwdirty vs. the swdirty setup is very similar, encouraging enough for me to ask our performance team to run a larger test. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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/