Public bug reported: Apologies if this is not the right forum to raise this concern. If not please point me to a better place to have this discussion.
The 5.3 linux kernel added a new feature which allows pages to be zeroed when allocating or freeing them: init_on_alloc and init_on_free. The init_on_alloc flag is enabled by default on the Ubuntu 18.04 HWE kernel. Linux kernel commit: https://github.com/torvalds/linux/commit/6471384af2a6530696fc0203bafe4de41a23c9ef ZFS allocates and frees pages frequently (via the ABD structure), e.g. for every disk access. The additional overhead of zeroing these pages is significant. For example, I measured a ~40% regression in performance of an uncached "zfs send ... >/dev/null". While this is a specific workload, this is a general problem because whenever we read from disk we are going to allocate pages, unnecessarily zero them, and then immediately fill them with the data from disk. I don't see any mechanism for ZFS to request that pages *not* be zeroed when they are allocated. This performance regression has been noted by users of ZFS on Ubuntu: https://github.com/zfsonlinux/zfs/issues/9910 I'd like to request that the default in Ubuntu be changed to init_on_alloc=0, so that users of ZFS on Ubuntu do not experience this performance regression. (FYI, my employer, Delphix, has worked around this by changing the default in our product, but my concern is that the vast majority of Ubuntu users will simply experience this as "Ubuntu HWE is much slower than before".) $ cat /proc/version_signature Ubuntu 5.3.0-28.30~18.04.1-generic 5.3.13 ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Attachment added: "lspci-vnvn.log" https://bugs.launchpad.net/bugs/1862822/+attachment/5327397/+files/lspci-vnvn.log -- 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/1862822 Title: init_on_alloc=1 causes big performance regression for ZFS Status in linux package in Ubuntu: New Bug description: Apologies if this is not the right forum to raise this concern. If not please point me to a better place to have this discussion. The 5.3 linux kernel added a new feature which allows pages to be zeroed when allocating or freeing them: init_on_alloc and init_on_free. The init_on_alloc flag is enabled by default on the Ubuntu 18.04 HWE kernel. Linux kernel commit: https://github.com/torvalds/linux/commit/6471384af2a6530696fc0203bafe4de41a23c9ef ZFS allocates and frees pages frequently (via the ABD structure), e.g. for every disk access. The additional overhead of zeroing these pages is significant. For example, I measured a ~40% regression in performance of an uncached "zfs send ... >/dev/null". While this is a specific workload, this is a general problem because whenever we read from disk we are going to allocate pages, unnecessarily zero them, and then immediately fill them with the data from disk. I don't see any mechanism for ZFS to request that pages *not* be zeroed when they are allocated. This performance regression has been noted by users of ZFS on Ubuntu: https://github.com/zfsonlinux/zfs/issues/9910 I'd like to request that the default in Ubuntu be changed to init_on_alloc=0, so that users of ZFS on Ubuntu do not experience this performance regression. (FYI, my employer, Delphix, has worked around this by changing the default in our product, but my concern is that the vast majority of Ubuntu users will simply experience this as "Ubuntu HWE is much slower than before".) $ cat /proc/version_signature Ubuntu 5.3.0-28.30~18.04.1-generic 5.3.13 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1862822/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
