I believe this bug is due to a change that causes files on a dax volume to be allocated as sparse files, so that every write to a new allocation unit causes another physical allocation. The previous behavior was to allocate the whole file up to the allocated size as one operation.
This is just by observing the behavior and running experiments to try to figure it out. I haven't looked at the code. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1848212 Title: Optane PM access times are much longer than they should be Status in linux package in Ubuntu: Confirmed Bug description: I have 4 128GB Optane DC Persistent Memory devices in my server, assigned to AppDirect access (i.e., accessed via memory-mapping at the cache line level), and have run into a severe performance issue with the latest kernel 5.0.0-31. I realize that not many people have this storage type as yet, but it is becoming increasingly important in the server world, so I think this bug is pretty important. Bug details: When running with kernel 5.0.0-29, write access times to the Optane PM devices are in the sub-microsecond range, as they should be. When running with kernel 5.0.0-31, write access times are much slower, averaging in the 30 microsecond range, until a large number of writes (see below) have been executed. Then they return to normal speed. My application is a hash table implementation optimized for the Optane PM devices (see webpage at www.threemisses.com). Since it is a hash table, it has very poor locality of reference, and is filled "randomly", so I don't know exactly what the sequence of writes is. However, I can say that the speed is very slow until the fill ratio of the hash table is about 50%, then it returns to the normal sub- microsecond range. ProblemType: Bug DistroRelease: Ubuntu 19.04 Package: linux-image-5.0.0-31-generic 5.0.0-31.33 ProcVersionSignature: Ubuntu 5.0.0-31.33-generic 5.0.21 Uname: Linux 5.0.0-31-generic x86_64 NonfreeKernelModules: nvidia_modeset nvidia ApportVersion: 2.20.10-0ubuntu27.1 Architecture: amd64 Date: Tue Oct 15 09:01:06 2019 InstallationDate: Installed on 2019-09-02 (42 days ago) InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416) IwConfig: lo no wireless extensions. eno0 no wireless extensions. enp181s0f1 no wireless extensions. MachineType: Supermicro SYS-7039A-I ProcEnviron: LD_LIBRARY_PATH=<set> TERM=xterm-256color PATH=(custom, no user) LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: 0 EFI VGA ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.0.0-31-generic root=UUID=3239f211-86a3-44bb-8251-62037ebea848 ro transparent_hugepage=always quiet splash nomodeset vt.handoff=1 PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon. RelatedPackageVersions: linux-restricted-modules-5.0.0-31-generic N/A linux-backports-modules-5.0.0-31-generic N/A linux-firmware 1.178.3 RfKill: SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 03/06/2019 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 3.0a dmi.board.asset.tag: ZM193S000653 dmi.board.name: X11DAi-N dmi.board.vendor: Supermicro dmi.board.version: 1.02 dmi.chassis.asset.tag: Default string dmi.chassis.type: 1 dmi.chassis.vendor: Supermicro dmi.chassis.version: 123456789 dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr3.0a:bd03/06/2019:svnSupermicro:pnSYS-7039A-I:pvr123456789:rvnSupermicro:rnX11DAi-N:rvr1.02:cvnSupermicro:ct1:cvr123456789: dmi.product.family: SMC X11 dmi.product.name: SYS-7039A-I dmi.product.sku: 097A15D9 dmi.product.version: 123456789 dmi.sys.vendor: Supermicro To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1848212/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
