I primarily test by building webkitgtk [1], and I experience the same loss of system responsiveness whether / is ext4 or Btrfs. But I do see a difference in top and iotop. https://drive.google.com/open?id=12jpQeskPsvHmfvDjWSPOwIWSz09JIUlk
This is an extreme case of refaulting, it's out of memory and swap, and since kswapd and btrfs threads are using a lot of CPU I'm guessing the faults are a mix of anonymous pages and file pages. At this point the system is really lost which is why the UX is the same with ext4 and btrfs; but behind the scenes it does seem more is going on. There might be other workloads which aren't as extreme, thereby exposing the difference. Two possible sources of the heavy CPU for btrfs threads: decompression, and checksumming. If it's true there is near constant reclaim happening, it's not just a simple minimum 4K read but rather a 128K minimum because all Btrfs compressed files use 128K extent size; is then decompressed, and then requires reading csum tree and computing csum on the read to compare. Ordinarily this is cheap but in this situation possibly it's resulting in a lot of extra congestion, but this is the limit of my knowledge so it's just speculation. Btrfs write amplification is a known issue (wandering trees problem). But that appears to not be the issue in this example. It might be this problem is better dealt with by cgroupsv2 to protect certain tasks from reclaim, and thus reduce the problem on any file system. But Btrfs alone (for now) does have more sophisticated cgroupvs2 IO isolation control as well. https://www.spinics.net/lists/cgroups/msg24743.html The upstream GNOME and KDE developers are aware of the loss of responsiveness problem and have done quite a lot of preliminary work in GNOME 3.34 with more work on the way. https://blogs.gnome.org/benzea/2019/10/01/gnome-3-34-is-now-managed-using-systemd/ You can today take advantage of this cgroupsv2 work by running resource hungry tasks as a systemd user unit in Fedora 31. https://blogs.gnome.org/benzea/2019/10/01/gnome-3-34-is-now-managed-using-systemd/#comment-14833 I expect in the next 6-12 months (it's a guesstimate) there will be additional work in GNOME to protect the user session or what I vaguely call the "GUI stack" from reclaim, and thus improve its responsiveness at the expense of the resource hungry process. [1] first two lines; set -j to RAM in GiB +2 GiB; i.e. if you have 8G RAM, use -j 10; more jobs makes the problem happen faster. https://trac.webkit.org/wiki/BuildingGtk -- 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/1833281 Title: System freeze when memory is put on SWAP in Linux >4.10.x Status in Linux: Confirmed Status in linux package in Ubuntu: Confirmed Bug description: I'm reporting this since it's reproduceable the 70% of the time. Summary: In different circumstances, when the systems starts to swap out RAM memory, even small amounts, the system becomes completely unusuable and the screen freezes up, no mouse movement, no TTY access or SSH access can be made, only SYSRQ keys seem to do something (only reboot, so REISUB worked so far though, OOM is useless since the memory/swap is not even full) The I/O Disk led is stuck to 100% in ALL the following cases when this happens. So far: - This happens even when only ZRAM is enabled, and no swap partition is used. - Happens when ZSWAP is used with a swap partition - Happens also when a partition without zram or zswap is used - Maybe it's AMD specific? However, I'm not experiencing this on my laptop using the same tests. My laptop is an Intel one, while my desktop is an AMD Ryzen platform. Here are the specs: CPU: AMD Ryzen 5 1600 no OC GPU: AMD RX 580 8GB SSD: Crucial MX500 500GB MOBO: MSI B350M Grenade RAM: 8GB HyperX Kingston 2667Mhz Ubuntu version: 18.04 LTS, backports repo enabled Kernel version: 4.18.0-18, official ubuntu repo Bios settings: Default Additional info: Maybe I'm not 100% sure, but I noticed when using the 5.0.0-17 generic kernel, the lockups seem to still happen, but they recover eventually. Happened only a few times though... But will always be frozen for at least 30 seconds, differently from my intel laptop where those do occur. The SSD make is the same. I bought two of these, they got also the same amount of RAM. In my laptop those do not occur at all. Swapping memory even huge quantities like 1GB or more, do not produce any issues. Tests made: For testing this behaviour I tried: - Compiling the chromium-browser source code (takes up a lot of system RAM) - Used the "stress" command, using a specific amount of memory to decide how many it will be swapped, and here I noticed that even small quantities like a couple of megabytes will cause the system to freeze the 70% of the times Example: "stress --vm 1 --vm-bytes=7G" What should happen: I expect system slowdowns when swapping out memory since I do not have enough RAM, but unlikely when using Windows or my laptop with the same Linux version, not a completely unusuable environment. The swap partition is in both cases on an SSD. Reproduceability: 70% of the times Additional info again: I'm not sure this is due to any hardware failure, my SSD health is fine, as my CPU and RAM. As I said swapping in Windows works fine... --- ProblemType: Bug ApportVersion: 2.20.9-0ubuntu7.6 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC1: haru 2076 F.... pulseaudio /dev/snd/controlC2: haru 2076 F.... pulseaudio /dev/snd/controlC0: haru 2076 F.... pulseaudio CurrentDesktop: communitheme:ubuntu:GNOME DistroRelease: Ubuntu 18.04 IwConfig: enp24s0 no wireless extensions. lo no wireless extensions. MachineType: Micro-Star International Co., Ltd. MS-7A37 Package: linux (not installed) ProcFB: 0 amdgpudrmfb ProcKernelCmdLine: BOOT_IMAGE=/@/boot/vmlinuz-5.0.0-17-generic root=UUID=75d45574-7169-4653-aea3-9f95087f0806 ro rootflags=subvol=@ quiet splash vt.handoff=1 ProcVersionSignature: Ubuntu 5.0.0-17.18~18.04.1-generic 5.0.8 RelatedPackageVersions: linux-restricted-modules-5.0.0-17-generic N/A linux-backports-modules-5.0.0-17-generic N/A linux-firmware 1.173.6 RfKill: 0: hci0: Bluetooth Soft blocked: no Hard blocked: no Tags: bionic Uname: Linux 5.0.0-17-generic x86_64 UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: sudo video WifiSyslog: _MarkForUpload: True dmi.bios.date: 01/22/2019 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 1.K0 dmi.board.asset.tag: To be filled by O.E.M. dmi.board.name: B350M MORTAR (MS-7A37) dmi.board.vendor: Micro-Star International Co., Ltd. dmi.board.version: 1.0 dmi.chassis.asset.tag: To be filled by O.E.M. dmi.chassis.type: 4 dmi.chassis.vendor: Micro-Star International Co., Ltd. dmi.chassis.version: 1.0 dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1.K0:bd01/22/2019:svnMicro-StarInternationalCo.,Ltd.:pnMS-7A37:pvr1.0:rvnMicro-StarInternationalCo.,Ltd.:rnB350MMORTAR(MS-7A37):rvr1.0:cvnMicro-StarInternationalCo.,Ltd.:ct4:cvr1.0: dmi.product.family: To be filled by O.E.M. dmi.product.name: MS-7A37 dmi.product.sku: To be filled by O.E.M. dmi.product.version: 1.0 dmi.sys.vendor: Micro-Star International Co., Ltd. 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