Deferred struct page init is a bottleneck in kernel boot--the biggest for us and probably others. Optimizing it maximizes availability for large-memory systems and allows spinning up short-lived VMs as needed without having to leave them running. It also benefits bare metal machines hosting VMs that are sensitive to downtime. In projects such as VMM Fast Restart[1], where guest state is preserved across kexec reboot, it helps prevent application and network timeouts in the guests. So, multithread deferred init to take full advantage of system memory bandwidth. Extend padata, a framework that handles many parallel singlethreaded jobs, to handle multithreaded jobs as well by adding support for splitting up the work evenly, specifying a minimum amount of work that's appropriate for one helper thread to do, load balancing between helpers, and coordinating them. More documentation in patches 4 and 7. This series is the first step in a project to address other memory proportional bottlenecks in the kernel such as pmem struct page init, vfio page pinning, hugetlb fallocate, and munmap. Deferred page init doesn't require concurrency limits, resource control, or priority adjustments like these other users will because it happens during boot when the system is otherwise idle and waiting for page init to finish. This has been run on a variety of x86 systems and speeds up kernel boot by 3% to 49%, saving up to 1.6 out of 4 seconds. Patch 5 has more numbers. Please review and test, and thanks to Alex, Andrew, Josh, and Pavel for their feedback in the last version. The powerpc and s390 lists are included in case they want to give this a try, they had enabled this feature when it was configured per arch. Series based on 5.7-rc6 plus these three from mmotm mm-call-touch_nmi_watchdog-on-max-order-boundaries-in-deferred-init.patch mm-initialize-deferred-pages-with-interrupts-enabled.patch mm-call-cond_resched-from-deferred_init_memmap.patch and it's available here: git://oss.oracle.com/git/linux-dmjordan.git padata-mt-definit-v2 https://oss.oracle.com/git/gitweb.cgi?p=linux-dmjordan.git;a=shortlog;h=refs/heads/padata-mt-definit-v2 and the future users and related features are available as work-in-progress: git://oss.oracle.com/git/linux-dmjordan.git padata-mt-wip-v0.4 https://oss.oracle.com/git/gitweb.cgi?p=linux-dmjordan.git;a=shortlog;h=refs/heads/padata-mt-wip-v0.4 v2: - Improve the problem statement (Andrew, Josh, Pavel) - Add T-b's to unchanged patches (Josh) - Fully initialize max-order blocks to avoid buddy issues (Alex) - Parallelize on section-aligned boundaries to avoid potential false sharing (Alex) - Return the maximum thread count from a function that architectures can override, with the generic version returning 1 (current behavior). Override for x86 since that's the only arch this series has been tested on so far. Other archs can test with more threads by dropping patch 6. - Rebase to v5.7-rc6, rerun tests RFC v4 [2] -> v1: - merged with padata (Peter) - got rid of the 'task' nomenclature (Peter, Jon) future work branch: - made lockdep-aware (Jason, Peter) - adjust workqueue worker priority with renice_or_cancel() (Tejun) - fixed undo problem in VFIO (Alex) The remaining feedback, mainly resource control awareness (cgroup etc), is TODO for later series. [1] https://static.sched.com/hosted_files/kvmforum2019/66/VMM-fast-restart_kvmforum2019.pdf https://www.youtube.com/watch?v=pBsHnf93tcQ https://lore.kernel.org/linux-mm/1588812129-8596-1-git-send-email-anthony.yznaga@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/20181105165558.11698-1-daniel.m.jordan@xxxxxxxxxx/ Daniel Jordan (7): padata: remove exit routine padata: initialize earlier padata: allocate work structures for parallel jobs from a pool padata: add basic support for multithreaded jobs mm: parallelize deferred_init_memmap() mm: make deferred init's max threads arch-specific padata: document multithreaded jobs Documentation/core-api/padata.rst | 41 +++-- arch/x86/mm/init_64.c | 12 ++ include/linux/memblock.h | 3 + include/linux/padata.h | 43 ++++- init/main.c | 2 + kernel/padata.c | 277 ++++++++++++++++++++++++------ mm/Kconfig | 6 +- mm/page_alloc.c | 67 +++++++- 8 files changed, 373 insertions(+), 78 deletions(-) base-commit: b9bbe6ed63b2b9f2c9ee5cbd0f2c946a2723f4ce prerequisite-patch-id: 4ad522141e1119a325a9799dad2bd982fbac8b7c prerequisite-patch-id: 169273327e56f5461101a71dfbd6b4cfd4570cf0 prerequisite-patch-id: 0f34692c8a9673d4c4f6a3545cf8ec3a2abf8620 -- 2.26.2
