From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga04.intel.com ([192.55.52.120]:30995 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754223AbdASTCe (ORCPT ); Thu, 19 Jan 2017 14:02:34 -0500 Date: Thu, 19 Jan 2017 11:59:11 -0700 From: Vishal Verma To: Jan Kara Cc: "Williams, Dan J" , "darrick.wong@oracle.com" , "Vyacheslav.Dubeyko@wdc.com" , "linux-nvdimm@ml01.01.org" , "linux-block@vger.kernel.org" , "slava@dubeyko.com" , "linux-fsdevel@vger.kernel.org" , "lsf-pc@lists.linux-foundation.org" Subject: Re: [Lsf-pc] [LSF/MM TOPIC] Badblocks checking/representation in filesystems Message-ID: <20170119185910.GF4880@omniknight.lm.intel.com> References: <20170114004910.GA4880@omniknight.lm.intel.com> <20170117143703.GP2517@quack2.suse.cz> <20170117221421.GC4880@omniknight.lm.intel.com> <20170118101641.GD24789@quack2.suse.cz> <20170118210241.GE10498@birch.djwong.org> <1484776549.4358.33.camel@intel.com> <20170119081011.GA2565@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170119081011.GA2565@quack2.suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 01/19, Jan Kara wrote: > On Wed 18-01-17 21:56:58, Verma, Vishal L wrote: > > On Wed, 2017-01-18 at 13:32 -0800, Dan Williams wrote: > > > On Wed, Jan 18, 2017 at 1:02 PM, Darrick J. Wong > > > wrote: > > > > On Wed, Jan 18, 2017 at 03:39:17PM -0500, Jeff Moyer wrote: > > > > > Jan Kara writes: > > > > > > > > > > > On Tue 17-01-17 15:14:21, Vishal Verma wrote: > > > > > > > Your note on the online repair does raise another tangentially > > > > > > > related > > > > > > > topic. Currently, if there are badblocks, writes via the bio > > > > > > > submission > > > > > > > path will clear the error (if the hardware is able to remap > > > > > > > the bad > > > > > > > locations). However, if the filesystem is mounted eith DAX, > > > > > > > even > > > > > > > non-mmap operations - read() and write() will go through the > > > > > > > dax paths > > > > > > > (dax_do_io()). We haven't found a good/agreeable way to > > > > > > > perform > > > > > > > error-clearing in this case. So currently, if a dax mounted > > > > > > > filesystem > > > > > > > has badblocks, the only way to clear those badblocks is to > > > > > > > mount it > > > > > > > without DAX, and overwrite/zero the bad locations. This is a > > > > > > > pretty > > > > > > > terrible user experience, and I'm hoping this can be solved in > > > > > > > a better > > > > > > > way. > > > > > > > > > > > > Please remind me, what is the problem with DAX code doing > > > > > > necessary work to > > > > > > clear the error when it gets EIO from memcpy on write? > > > > > > > > > > You won't get an MCE for a store;��only loads generate them. > > > > > > > > > > Won't fallocate FL_ZERO_RANGE clear bad blocks when mounted with > > > > > -o dax? > > > > > > > > Not necessarily; XFS usually implements this by punching out the > > > > range > > > > and then reallocating it as unwritten blocks. > > > > > > > > > > That does clear the error because the unwritten blocks are zeroed and > > > errors cleared when they become allocated again. > > > > Yes, the problem was that writes won't clear errors. zeroing through > > either hole-punch, truncate, unlinking the file should all work > > (assuming the hole-punch or truncate ranges wholly contain the > > 'badblock' sector). > > Let me repeat my question: You have mentioned that if we do IO through DAX, > writes won't clear errors and we should fall back to normal block path to > do write to clear the error. What does prevent us from directly clearing > the error from DAX path? > With DAX, all IO goes through DAX paths. There are two cases: 1. mmap and loads/stores: Obviously there is no kernel intervention here, and no badblocks handling is possible. 2. read() or write() IO: In the absence of dax, this would go through the bio submission path, through the pmem driver, and that would handle error clearing. With DAX, this goes through dax_iomap_actor, which also doesn't go through the pmem driver (it does a dax mapping, followed by essentially memcpy), and hence cannot handle badblocks. > Honza > -- > Jan Kara > SUSE Labs, CR