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Wong" , Brian Foster , "hch@infradead.org" CC: =?UTF-8?B?UnVhbiwgU2hpeWFuZy/pmK4g5LiW6Ziz?= , "linux-kernel@vger.kernel.org" , "linux-xfs@vger.kernel.org" , "nvdimm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "david@fromorbit.com" , "hch@infradead.org" References: <7fde89dc-2e8f-967b-d342-eb334e80255c@fujitsu.com> <0ea1cbe1-79d7-c22b-58bf-5860a961b680@fujitsu.com> <7fdc9e88-f255-6edb-7964-a5a82e9b1292@fujitsu.com> <76ea04b4-bad7-8cb3-d2c6-4ad49def4e05@fujitsu.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.167.215.54] X-ClientProxiedBy: G08CNEXCHPEKD07.g08.fujitsu.local (10.167.33.80) To R01UKEXCASM121.r01.fujitsu.local (10.183.43.173) X-Virus-Scanned: ClamAV using ClamSMTP Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 2022/9/15 18:14, Yang, Xiao/杨 晓 wrote: > On 2022/9/15 0:28, Darrick J. Wong wrote: >> On Wed, Sep 14, 2022 at 08:34:26AM -0400, Brian Foster wrote: >>> On Wed, Sep 14, 2022 at 05:38:02PM +0800, Yang, Xiao/杨 晓 wrote: >>>> On 2022/9/14 14:44, Yang, Xiao/杨 晓 wrote: >>>>> On 2022/9/9 21:01, Brian Foster wrote: >>>>>> Yes.. I don't recall all the internals of the tools and test, but >>>>>> IIRC >>>>>> it relied on discard to perform zeroing between checkpoints or >>>>>> some such >>>>>> and avoid spurious failures. The purpose of running on dm-thin was >>>>>> merely to provide reliable discard zeroing behavior on the target >>>>>> device >>>>>> and thus to allow the test to run reliably. >>>>> Hi Brian, >>>>> >>>>> As far as I know, generic/470 was original designed to verify >>>>> mmap(MAP_SYNC) on the dm-log-writes device enabling DAX. Due to the >>>>> reason, we need to ensure that all underlying devices under >>>>> dm-log-writes device support DAX. However dm-thin device never >>>>> supports >>>>> DAX so >>>>> running generic/470 with dm-thin device always returns "not run". >>>>> >>>>> Please see the difference between old and new logic: >>>>> >>>>>             old logic                          new logic >>>>> --------------------------------------------------------------- >>>>> log-writes device(DAX)                 log-writes device(DAX) >>>>>               |                                       | >>>>> PMEM0(DAX) + PMEM1(DAX)       Thin device(non-DAX) + PMEM1(DAX) >>>>>                                             | >>>>>                                           PMEM0(DAX) >>>>> --------------------------------------------------------------- >>>>> >>>>> We think dm-thin device is not a good solution for generic/470, is >>>>> there >>>>> any other solution to support both discard zero and DAX? >>>> >>>> Hi Brian, >>>> >>>> I have sent a patch[1] to revert your fix because I think it's not >>>> good for >>>> generic/470 to use thin volume as my revert patch[1] describes: >>>> [1] >>>> https://lore.kernel.org/fstests/20220914090625.32207-1-yangx.jy@fujitsu.com/T/#u >>>> >>>> >>> >>> I think the history here is that generic/482 was changed over first in >>> commit 65cc9a235919 ("generic/482: use thin volume as data device"), and >>> then sometime later we realized generic/455,457,470 had the same general >>> flaw and were switched over. The dm/dax compatibility thing was probably >>> just an oversight, but I am a little curious about that because it >>> should >> >> It's not an oversight -- it used to work (albeit with EXPERIMENTAL >> tags), and now we've broken it on fsdax as the pmem/blockdev divorce >> progresses. > Hi > > Do you mean that the following patch set changed the test result of > generic/470 with thin-volume? (pass => not run/failure) > https://lore.kernel.org/linux-xfs/20211129102203.2243509-1-hch@lst.de/ > >> >>> have been obvious that the change caused the test to no longer run. Did >>> something change after that to trigger that change in behavior? >>> >>>> With the revert, generic/470 can always run successfully on my >>>> environment >>>> so I wonder how to reproduce the out-of-order replay issue on XFS v5 >>>> filesystem? >>>> >>> >>> I don't quite recall the characteristics of the failures beyond that we >>> were seeing spurious test failures with generic/482 that were due to >>> essentially putting the fs/log back in time in a way that wasn't quite >>> accurate due to the clearing by the logwrites tool not taking place. If >>> you wanted to reproduce in order to revisit that, perhaps start with >>> generic/482 and let it run in a loop for a while and see if it >>> eventually triggers a failure/corruption..? >>> >>>> PS: I want to reproduce the issue and try to find a better solution >>>> to fix >>>> it. >>>> >>> >>> It's been a while since I looked at any of this tooling to semi-grok how >>> it works. >> >> I /think/ this was the crux of the problem, back in 2019? >> https://lore.kernel.org/fstests/20190227061529.GF16436@dastard/ > > Agreed. > >> >>> Perhaps it could learn to rely on something more explicit like >>> zero range (instead of discard?) or fall back to manual zeroing? >> >> AFAICT src/log-writes/ actually /can/ do zeroing, but (a) it probably >> ought to be adapted to call BLKZEROOUT and (b) in the worst case it >> writes zeroes to the entire device, which is/can be slow. >> >> For a (crass) example, one of my cloudy test VMs uses 34GB partitions, >> and for cost optimization purposes we're only "paying" for the cheapest >> tier.  Weirdly that maps to an upper limit of 6500 write iops and >> 48MB/s(!) but that would take about 20 minutes to zero the entire >> device if the dm-thin hack wasn't in place.  Frustratingly, it doesn't >> support discard or write-zeroes. > > Do you mean that discard zero(BLKDISCARD) is faster than both fill > zero(BLKZEROOUT) and write zero on user space? Hi Darrick, Brian and Christoph According to the discussion about generic/470. I wonder if it is necessary to make thin-pool support DAX. Is there any use case for the requirement? Best Regards, Xiao Yang > > Best Regards, > Xiao Yang >> >>> If the >>> eventual solution is simple and low enough overhead, it might make some >>> sense to replace the dmthin hack across the set of tests mentioned >>> above. >> >> That said, for a *pmem* test you'd expect it to be faster than that... >> >> --D >> >>> Brian >>> >>>> Best Regards, >>>> Xiao Yang >>>> >>>>> >>>>> BTW, only log-writes, stripe and linear support DAX for now. >>>> >>>