From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: regression introduced by "block: Add support for DAX reads/writes to block devices" Date: Thu, 13 Aug 2015 13:14:49 -0400 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Boaz Harrosh , "Wilcox\, Matthew R" , "linux-kernel\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , "Vishal L. Verma" To: Linda Knippers Return-path: In-Reply-To: <55CCC8F8.6080204@hp.com> (Linda Knippers's message of "Thu, 13 Aug 2015 12:42:32 -0400") Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.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=E2=80=99s preferred minimum unit for random I/= O See Martin Petersen's "Linux & Advanced Storage Interfaces" document fo= r 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 o= f 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 fo= r testing. Do we care about breaking that? Cheers, Jeff