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b1029f29eb
Patch series "mm/damon: strictly respect min_nr_regions". DAMON core respects min_nr_regions only at merge operation. DAMON API callers are therefore responsible to respect or ignore that. Only vaddr ops is respecting that, but only for initial start time. DAMON sysfs interface allows users to setup the initial regions that DAMON core also respects. But, again, it works for only the initial time. Users setting the regions for min_nr_regions can be difficult and inefficient, when the min_nr_regions value is high. There was actually a report [1] from a user. The use case was page granular access monitoring with a large aggregation interval. Make the following three changes for resolving the issue. First (patch 1), make DAMON core split regions at the beginning and every aggregation interval, to respect the min_nr_regions. Second (patch 2), drop the vaddr's split operations and related code that are no more needed. Third (patch 3), add a kunit test for the newly introduced function. This patch (of 3): DAMON core layer respects the min_nr_regions parameter by setting the maximum size of each region as total monitoring region size divided by the parameter value. And the limit is applied by preventing merge of regions that result in a region larger than the maximum size. The limit is updated per ops update interval, because vaddr updates the monitoring regions on the ops update callback. It does nothing for the beginning state. That's because the users can set the initial monitoring regions as they want. That is, if the users really care about the min_nr_regions, they are supposed to set the initial monitoring regions to have more than min_nr_regions regions. The virtual address space operation set, vaddr, has an exceptional case. Users can ask the ops set to configure the initial regions on its own. For the case, vaddr sets up the initial regions to meet the min_nr_regions. So, vaddr has exceptional support, but basically users are required to set the regions on their own if they want min_nr_regions to be respected. When 'min_nr_regions' is high, such initial setup is difficult. If DAMON sysfs interface is used for that, the memory for saving the initial setup is also a waste. Even if the user forgives the setup, DAMON will eventually make more than min_nr_regions regions by splitting operations. But it will take time. If the aggregation interval is long, the delay could be problematic. There was actually a report [1] of the case. The reporter wanted to do page granular monitoring with a large aggregation interval. Also, DAMON is doing nothing for online changes on monitoring regions and min_nr_regions. For example, the user can remove a monitoring region or increase min_nr_regions while DAMON is running. Split regions larger than the size at the beginning of the kdamond main loop, to fix the initial setup issue. Also do the split every aggregation interval, for online changes. This means the behavior is slightly changed. It is difficult to imagine a use case that actually depends on the old behavior, though. So this change is arguably fine. Note that the size limit is aligned by damon_ctx->min_region_sz and cannot be zero. That is, if min_nr_region is larger than the total size of monitoring regions divided by ->min_region_sz, that cannot be respected. Link: https://lkml.kernel.org/r/20260228222831.7232-1-sj@kernel.org Link: https://lkml.kernel.org/r/20260228222831.7232-2-sj@kernel.org Link: https://lore.kernel.org/CAC5umyjmJE9SBqjbetZZecpY54bHpn2AvCGNv3aF6J=1cfoPXQ@mail.gmail.com [1] Signed-off-by: SeongJae Park <sj@kernel.org> Cc: Brendan Higgins <brendan.higgins@linux.dev> Cc: David Gow <davidgow@google.com> 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. 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