From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753532AbcEPMpF (ORCPT ); Mon, 16 May 2016 08:45:05 -0400 Received: from a.ns.miles-group.at ([95.130.255.143]:11950 "EHLO radon.swed.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753348AbcEPMpC (ORCPT ); Mon, 16 May 2016 08:45:02 -0400 Subject: Re: UBIFS and page migration (take 3) To: Christoph Hellwig References: <1462974823-3168-1-git-send-email-richard@nod.at> <20160512114948.GA25113@infradead.org> Cc: linux-fsdevel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, boris.brezillon@free-electrons.com, maxime.ripard@free-electrons.com, david@sigma-star.at, david@fromorbit.com, dedekind1@gmail.com, alex@nextthing.co, akpm@linux-foundation.org, sasha.levin@oracle.com, iamjoonsoo.kim@lge.com, rvaswani@codeaurora.org, tony.luck@intel.com, shailendra.capricorn@gmail.com, kirill.shutemov@linux.intel.com, hughd@google.com, mgorman@techsingularity.net, vbabka@suse.cz From: Richard Weinberger Message-ID: <5739C0C1.1090907@nod.at> Date: Mon, 16 May 2016 14:44:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <20160512114948.GA25113@infradead.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christoph, Am 12.05.2016 um 13:49 schrieb Christoph Hellwig: > Hi Richard, > > the series looks fine to me, but it fails to address the root cause: Is this a Reviewed-by? :-) > that we have an inherently dangerous default for ->migratepage that > assumes that file systems are implemented a certain way. I think the > series should also grow a third patch to remove the default and just > wire it up for the known good file systems, although we'd need some > input on what known good is. > > Any idea what filesystems do get regular testing with code that's using > CMA? A good approximation might be those that use the bufer_head > based aops from fs/buffer.c No idea how much is being tested. I fear most issues are unknown. At least for UBIFS it took years to get aware of the issue. Thanks again to Maxime and Boris for providing a reproducer. There are two classes of issues: a) filesystems that use buffer_migrate_page() but shouldn't b) filesystems that don't implement ->migratepage() and fallback_migrate_page() is not suitable. As starter we could kill the automatic assignment of fallback_migrate_page() and non-buffer_head filesystems need to figure out whether fallback_migrate_page() is suitable or not. UBIFS found out the hard way. ;-\ MM folks, do we have a way to force page migration? Maybe we can create a generic stress test. Thanks, //richard