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Wong" , Brian Foster 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> From: =?UTF-8?B?WWFuZywgWGlhby/mnagg5pmT?= 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-kernel@vger.kernel.org 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? 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. >>> >>