From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753469AbbHMROx (ORCPT ); Thu, 13 Aug 2015 13:14:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53556 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753318AbbHMROv convert rfc822-to-8bit (ORCPT ); Thu, 13 Aug 2015 13:14:51 -0400 From: Jeff Moyer To: Linda Knippers Cc: Boaz Harrosh , "Wilcox\, Matthew R" , "linux-kernel\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , "Vishal L. Verma" Subject: Re: regression introduced by "block: Add support for DAX reads/writes to block devices" References: <100D68C7BA14664A8938383216E40DE04091408C@FMSMSX114.amr.corp.intel.com> <100D68C7BA14664A8938383216E40DE0409144D9@FMSMSX114.amr.corp.intel.com> <55C855D5.1070001@plexistor.com> <55CC2BDA.3080906@plexistor.com> <55CCC8F8.6080204@hp.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Thu, 13 Aug 2015 13:14:49 -0400 In-Reply-To: <55CCC8F8.6080204@hp.com> (Linda Knippers's message of "Thu, 13 Aug 2015 12:42:32 -0400") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linda Knippers writes: >> I'd be fine with changing the persistent memory block device to only >> support 4k logical, 4k physical block size. That probably makes the >> most sense. > > If that's what we want, the current patch doesn't do that. > https://lists.01.org/pipermail/linux-nvdimm/2015-July/001555.html > > It causes the physical block size to be PAGE_SIZE but the > logical block size is still 512. However, the minimum_io_size > is now 4096 (same as physical block size, I assume). The > optimal_io_size is still 0. What does that mean? physical block size - device's internal block size logical block size - addressable unit optimal io size - device's preferred unit for streaming minimum io size - device’s preferred minimum unit for random I/O See Martin Petersen's "Linux & Advanced Storage Interfaces" document for more information. > Whatever we go with, we should do something because 4.2rc6 is still > broken, unable to create a xfs file system on a pmem device, ever > since the change to use DAX on block devices with O_DIRECT. We can change the block device to export logical/physical block sizes of PAGE_SIZE. However, when persistent memory support comes to platforms that support page sizes > 32k, xfs will again run into problems (Dave Chinner mentioned that xfs can't deal with logical block sizes >32k.) Arguably, you can use pmem and dax on such platforms using RAM today for testing. Do we care about breaking that? Cheers, Jeff