From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kani, Toshi" Subject: Re: [PATCH v2 5/7] dm: remove DM_TYPE_DAX_BIO_BASED dm_queue_mode Date: Mon, 4 Jun 2018 23:49:18 +0000 Message-ID: <1528156065.14039.113.camel@hpe.com> References: <20180529195106.14268-1-ross.zwisler@linux.intel.com> <20180529195106.14268-6-ross.zwisler@linux.intel.com> <20180601220443.GB18712@redhat.com> <20180604232416.GB10666@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180604232416.GB10666-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> Content-Language: en-US Content-ID: <1D4ACA0B174EA340BD68FDA59FFD6084-mmYPd6ayCNGroOM5E8FhRbjFIynDaujOfM0AETQt39g@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: "ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org" , "snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" Cc: "linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-xfs-u79uwXL29TYaXLmJjATzhQ@public.gmane.org" , "linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org" List-Id: dm-devel.ids On Mon, 2018-06-04 at 17:24 -0600, Ross Zwisler wrote: > On Fri, Jun 01, 2018 at 06:04:43PM -0400, Mike Snitzer wrote: > > On Tue, May 29 2018 at 3:51pm -0400, > > Ross Zwisler wrote: : > > For example, the following transition will currently fail: > > > > dm-linear: [fsdax pmem][fsdax pmem] => [fsdax pmem][fsdax raw] > > DM_TYPE_DAX_BIO_BASED DM_TYPE_BIO_BASED > > > > but these will both succeed: > > > > dm-linear: [fsdax pmem][brd ramdisk] => [fsdax pmem][fsdax raw] > > DM_TYPE_BIO_BASED DM_TYPE_BIO_BASED > > > > dm-linear: [fsdax pmem][fsdax raw] => [fsdax pmem][fsdax pmem] > > DM_TYPE_BIO_BASED DM_TYPE_DAX_BIO_BASED > > So we allow 2 of the 3 transitions, but the reason that we disallow the third > isn't fully clear to me. I need to refresh my memory for the code, but here is the intent. https://lkml.org/lkml/2016/6/22/1000 https://lkml.org/lkml/2016/6/22/999 > > > dm-linear: [fsdax pmem][fsdax raw] => [fsdax pmem][fsdax pmem] > > > DM_TYPE_BIO_BASED DM_TYPE_DAX_BIO_BASED > > > > > > This seems arbitrary, as really the choice on whether to use DAX happens at > > > filesystem mount time. There's no guarantee that the in the first case > > > (double fsdax pmem) we were using the dax mount option with our file > > > system. > > > > > > Instead, get rid of DM_TYPE_DAX_BIO_BASED and all the special casing around > > > it, and instead make the request queue's QUEUE_FLAG_DAX be our one source > > > of truth. If this is set, we can use DAX, and if not, not. We keep this > > > up to date in table_load() as the table changes. As with regular block > > > devices the filesystem will then know at mount time whether DAX is a > > > supported mount option or not. > > > > If you don't think you need this specialization that is fine.. but DM > > devices supporting suspending (as part of table reloads) so is there any > > risk that there will be inflight IO (say if someone did 'dmsetup suspend > > --noflush').. and then upon reload the device type changed out from > > under us.. anyway, I don't have all the PMEM DAX stuff paged back into > > my head yet. > > > > But this just seems like we really shouldn't be allowing the > > transition from what was DM_TYPE_DAX_BIO_BASED back to DM_TYPE_BIO_BASED > > I admit I don't fully understand all the ways that DM supports suspending and > resuming devices. Is there actually a case where we can change out the DM > devices while I/O is running, and somehow end up trying to issue a DAX I/O to > a device that doesn't support DAX? > > Toshi, do you have a test case that shows this somehow? No, I did not test suspend/resume since HPE servers do not support it. Thanks, -Toshi