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Patch series "mm/damon: introduce data attributes monitoring". TL; DR ====== Extend DAMON for monitoring general data attributes other than accesses. The short term motivation is lightweight page type (e.g., belonging cgroup) aware monitoring. In long term, this will help extending DAMON for multiple access events capture primitives (e.g., page faults and PMU) and eventually pivotting DAMON to a "Data Attributes Monitoring and Operations eNgine" in long term. Background: High Cost of Page Level Properties Monitoring ========================================================= DAMON is initially introduced as a Data Access MONitor. It has been extended for not only access monitoring but also data access-aware system operations (DAMOS). But still the monitoring part is only for data accesses. Data access patterns is good information, but some users need more holistic views. Particularly, users want to show the access pattern information together with the types of the memory. For example, users who work for making huge pages efficiently want to know how much of DAMON-found hot/cold regions are backed by huge pages. Users who run multiple workloads with different cgroups want to know how much of DAMON-found hot/cold regions belong to specific cgroups. For the user demand, we developed a DAMOS extension for page level properties based monitoring [1], which has landed on 6.14. Using the feature, users can inform the page level data properties that they are interested in, in a flexible format that uses DAMOS filters. Then, DAMON applies the filters to each folio of the entire DAMON region and lets users know how many bytes of memory in each DAMON region passed the given filters. This gives page level detailed and deterministic information to users. But, because the operation is done at page level, the overhead is proportional to the memory size. It was useful for test or debugging purposes on a small number of machines. But it was obviously too heavy to be enabled always on all machines running the real user workloads. For real world workloads, it was recommended to use the feature with user-space controlled sampling approaches. For example, users could do the page level monitoring only once per hour, on randomly selected one percent of machines of their fleet. If the runtime and the size of the fleet is long and big enough, it should provide statistically meaningful data. But users are too busy to implement such controls on their own. Data Attributes Monitoring ========================== Extend DAMON to monitor not only data accesses, but also general data attributes. Do the extension while keeping the main promise of DAMON, the bounded and best-effort minimum overhead. Allow users to specify what data attributes in addition to the data access they want to monitor. Users can install one 'data probe' per data attribute of their interest for this purpose. The 'data probe' should be able to be applied to any memory, and determine if the given memory has the appropriate data attribute. E.g., if memory of physical address 42 belongs to cgroup A. Each 'data probe' is configured with filters that are very similar to the DAMOS filters. When DAMON checks if each sampling address memory of each region is accessed since the last check, it applies data probes if registered. Same to the number of access check-positive samples accounting (nr_accesses), it accounts the number of each data probe-positive samples in another per-region counters array, namely 'probe_hits'. When DAMON resets nr_accesses every aggregation interval, it resets 'probe_hits' together. Users can read 'probe_hits' just before the values are reset. In this way, users can know how many hot/cold memory regions have data attributes of their interest. E.g., 30 percent of this system's hot memory is belonging to cgroup A, and 80 percent of the cgroup A-belonging hot memory is backed by huge pages. Patches Sequence ================ First eight patches implement the core feature, interface and the working support. Patch 1 introduces data probe data structure, namely damon_probe. Patch 2 extends damon_ctx for installing data probes. Patch 3 introduces another data structure for filters of each data probe, namely damon_filter. Patch 4 updates damon_ctx commit function to handle the probes. Patch 5 extends damon_region for the per-region per-probe positive samples counter, namely probe_hits. Patch 6 extends damon_operations for applying probes on the underlying DAMON operations implementation. Patch 7 updates kdamond_fn() to invoke the probes applying callback. Patch 8 finally implements the probes support on paddr ops. Ten changes for user interface (patches 9-18) come next. Patches 9-13 implements sysfs directories and files for setting data probes, namely probes directory, probe directory, filters directory, filter directory and filter directory internal files, respectively. Patch 14 connects the user inputs that are made via the sysfs files to DAMON core. Following three patches (patches 15-17) implement sysfs directories and files for showing the probe_hits to users, namely probes directory, probe directory and hits files, respectively. Patch 18 introduces a new tracepoint for showing the probe_hits via tracefs. Patch 19 adds a selftest for the sysfs files. Patches 20 and 21 documents the design and usage of the new feature, respectively. Seven additional patches (patches 22-28) for monitoring belonging memory cgroup follow. Depending on the feedback, this part might be separated to another series in future. Patch 22 defines the DAMON filter type for the new attribute, namely DAMON_FILTER_TYPE_MEMCG. Patch 23 add the support on paddr ops. Patch 24 updates the sysfs interface for setup of the target memcg. Patch 25 move code for easy reuse of the filter target memcg setup. Patch 26 connects the user input to the core layer. Finally, patches 27 and 28 update the design and usage documents for the memcg attribute monitoring support. Discussion ========== This allows the page properties monitoring with overhead that is low enough to be enabled always on real world workloads. Because the sampling time for access check is reused for data attributes check, the upper-bounded and best-effort minimum overhead of DAMON is kept. Because the sampling memory for access check is reused for data attributes check, additional overhead is minimum. Still DAMOS-based page level properties monitoring should be useful, because it provides a deterministic page level information. When in doubt of the sampling based information, running DAMOS-based one together and comparing the results would be useful, for debugging and tuning. Future Works: Mid Term ======================== This version of implementation is limiting the maximum number of data probes to four. I will try to find a way to remove the limit in future. I personally think it should be enough for common use cases, though, and therefore not giving high priority at the moment. Future Works: Long Term ======================= There are user requests for extending DAMON with detailed access information, for example, per-CPUs/threads/read/writes monitoring. For that, I was working [2] on extending DAMON to use page fault events as another access check primitives, and making the infrastructure flexible for future use of yet another access check primitive. Actually there is another ongoing work [3] for extending DAMON with PMU events. The motivation of the work is reducing the overhead, though. In my work [2], I was introducing a new interface for access sampling primitives control. Now I think this data probe interface can be used for that, too. That is, data access becomes just one type of data attribute. Also, pg_idle-confirmed access, page fault-confirmed access, and PMU event-confirmed access will be different types of data attributes. The regions adjustment mechanism is currently working based on the access information. That's because DAMON is designed for data access monitoring. That is, data access information is the primary interest, and therefore DAMON adjusts regions in a way that can best-present the information. Once data access becomes just one of data attributes, there is no reason to think data access that special. There might be some users not interested in access at all but want to know the location of memory of specific type. Data probes interface will allow doing that. Further, we could extend the interface to let users set any data attribute as the 'primary' attribute. Then, DAMON will split and merge regions in a way that can best-present the 'primary' attributes. DAMOS will also be extended, to specify targets based on not only the data access pattern, but all user-registered data attributes. From this stage, we may be able to call DAMON as a "Data Attributes Monitoring and Operations eNgine". This patch (of 28): Introduce a data structure for data attribute probe. It is just a linked list header at this step. It will be extended in a way that it can determine if a given memory has a specific data attribute. Link: https://lore.kernel.org/20260518234119.97569-1-sj@kernel.org Link: https://lore.kernel.org/20260518234119.97569-2-sj@kernel.org Link: https://lore.kernel.org/20250106193401.109161-1-sj@kernel.org [1] Link: https://lore.kernel.org/20251208062943.68824-1-sj@kernel.org/ [2] Link: https://lore.kernel.org/20260423004211.7037-1-akinobu.mita@gmail.com [3] Signed-off-by: SeongJae Park <sj@kernel.org> Cc: David Hildenbrand <david@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Liam R. Howlett <liam@infradead.org> Cc: Lorenzo Stoakes <ljs@kernel.org> Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@kernel.org> 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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