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3bc181c143
Patch series "mm/mprotect: micro-optimization work", v3. Micro-optimize the change_protection functionality and the change_pte_range() routine. This set of functions works in an incredibly tight loop, and even small inefficiencies are incredibly evident when spun hundreds, thousands or hundreds of thousands of times. There was an attempt to keep the batching functionality as much as possible, which introduced some part of the slowness, but not all of it. Removing it for !arm64 architectures would speed mprotect() up even further, but could easily pessimize cases where large folios are mapped (which is not as rare as it seems, particularly when it comes to the page cache these days). The micro-benchmark used for the tests was [0] (usable using google/benchmark and g++ -O2 -lbenchmark repro.cpp) This resulted in the following (first entry is baseline): --------------------------------------------------------- Benchmark Time CPU Iterations --------------------------------------------------------- mprotect_bench 85967 ns 85967 ns 6935 mprotect_bench 70684 ns 70684 ns 9887 After the patchset we can observe an ~18% speedup in mprotect. Wonderful for the elusive mprotect-based workloads! Testing & more ideas welcome. I suspect there is plenty of improvement possible but it would require more time than what I have on my hands right now. The entire inlined function (which inlines into change_protection()) is gigantic - I'm not surprised this is so finnicky. Note: per my profiling, the next _big_ bottleneck here is modify_prot_start_ptes, exactly on the xchg() done by x86. ptep_get_and_clear() is _expensive_. I don't think there's a properly safe way to go about it since we do depend on the D bit quite a lot. This might not be such an issue on other architectures. Luke Yang reported [1]: : On average, we see improvements ranging from a minimum of 5% to a : maximum of 55%, with most improvements showing around a 25% speed up in : the libmicro/mprot_tw4m micro benchmark. This patch (of 2): Move softleaf change_pte_range code into a separate function. This makes the change_pte_range() function a good bit smaller, and lessens cognitive load when reading through the function. Link: https://lore.kernel.org/20260402141628.3367596-1-pfalcato@suse.de Link: https://lore.kernel.org/20260402141628.3367596-2-pfalcato@suse.de Link: https://lore.kernel.org/all/aY8-XuFZ7zCvXulB@luyang-thinkpadp1gen7.toromso.csb/ Link: https://gist.github.com/heatd/1450d273005aba91fa5744f44dfcd933 [0] Link: https://lore.kernel.org/CAL2CeBxT4jtJ+LxYb6=BNxNMGinpgD_HYH5gGxOP-45Q2OncqQ@mail.gmail.com [1] Signed-off-by: Pedro Falcato <pfalcato@suse.de> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Tested-by: Luke Yang <luyang@redhat.com> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Jann Horn <jannh@google.com> Cc: Jiri Hladky <jhladky@redhat.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst