From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga03.intel.com ([134.134.136.65]:46039 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752676AbeFZTLb (ORCPT ); Tue, 26 Jun 2018 15:11:31 -0400 Date: Tue, 26 Jun 2018 13:11:29 -0600 From: Ross Zwisler To: Mike Snitzer Cc: Dan Williams , Ross Zwisler , Toshi Kani , device-mapper development , linux-nvdimm , Linux Kernel Mailing List , stable , linux-xfs , linux-fsdevel Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode Message-ID: <20180626191129.GA18273@linux.intel.com> References: <20180626175932.8899-1-ross.zwisler@linux.intel.com> <20180626175932.8899-2-ross.zwisler@linux.intel.com> <20180626185830.GA7171@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180626185830.GA7171@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jun 26, 2018 at 02:58:30PM -0400, Mike Snitzer wrote: > On Tue, Jun 26 2018 at 2:52pm -0400, > Dan Williams wrote: > > > On Tue, Jun 26, 2018 at 10:59 AM, Ross Zwisler > > wrote: > > > QUEUE_FLAG_DAX is an indication that a given block device supports > > > filesystem DAX and should not be set for PMEM namespaces which are in "raw" > > > or "sector" modes. These namespaces lack struct page and are prevented > > > from participating in filesystem DAX. > > > > > > Signed-off-by: Ross Zwisler > > > Suggested-by: Mike Snitzer > > > Cc: stable@vger.kernel.org > > > > Why is this cc: stable? What is the user visible impact of this change > > especially given the requirement to validate QUEUE_FLAG_DAX with > > bdev_dax_supported()? Patch looks good, but it's just a cosmetic fixup > > afaics. > > This isn't cosmetic when you consider that stacking up a DM device is > looking at this flag to determine whether a table does or does _not_ > support DAX. > > So this patch, in conjunction with the other changes in the series, is > certainly something I'd consider appropriate for stable. > > Mike Because in patch 3 of this series we now use the full bdev_dax_supported() instead of just checking the queue flag in device_supports_dax(), I agree that this isn't strictly necessary for stable. device_supports_dax() will still notice that the raw/sector namespaces don't support DAX because bdev_dax_supported() will fail, and we'll end up doing the right thing and not setting QUEUE_FLAG_DAX on the DM device. I think maybe it's good to have in stable for completeness (and it's a very small change), but if we drop it from stable the code will still do the right thing AFAICT.