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MGLRU gives high priority to folios mapped in page tables. As a result, folio_set_active() is invoked for all folios read during page faults. In practice, however, readahead can bring in many folios that are never accessed via page tables. A previous attempt by Lei Liu proposed introducing a separate LRU for readahead[1] to make readahead pages easier to reclaim, but that approach is likely over-engineered. Before commit4d5d14a01e("mm/mglru: rework workingset protection"), folios with PG_active were always placed in the youngest generation, leading to over-protection and increased refaults. After that commit, PG_active folios are placed in the second youngest generation, which is still too optimistic given the presence of readahead. In contrast, the classic active/inactive scheme is more conservative. This patch switches to using folio_mark_accessed() and begins prefaulted file folios from the second oldest generation instead of active generations. We should also adjust the following accordingly: - WORKINGSET_ACTIVATE: aligned with setting active for refaulted workingset folios; - lru_gen_folio_seq(): place (pre)faulted file folios into the second oldest generation; - promote second-scanned folios to workingset in folio_check_references(): we now have to depend on folio_lru_refs() > 1, since we previously relied on PG_referenced being set during the first scan, but PG_referenced is now set earlier. On x86, running a kernel build inside a memcg with a 1GB memory limit using 20 threads. w/o patch: real 1m50.764s user 25m32.305s sys 4m0.012s pswpin: 1333245 pswpout: 4366443 pgpgin: 6962592 pgpgout: 17780712 swpout_zero: 1019603 swpin_zero: 14764 refault_file: 287794 refault_anon: 1347963 w/ patch: real 1m48.879s user 25m29.224s sys 3m37.421s pswpin: 568480 pswpout: 2322657 pgpgin:4073416pgpgout: 9613408 swpout_zero: 593275 swpin_zero: 9118 refault_file: 262505 refault_anon: 577550 active/inactive LRU: real 1m49.928s user 25m28.196s sys 3m40.740s pswpin: 463452 pswpout: 2309119 pgpgin:4438856pgpgout: 9568628 swpout_zero: 743704 swpin_zero: 7244 refault_file: 562555 refault_anon: 470694 Lance and Xueyuan made a huge contribution to this patch through testing. Link: https://lore.kernel.org/20260526130938.66253-1-baohua@kernel.org Link: https://lore.kernel.org/linux-mm/20250916072226.220426-1-liulei.rjpt@vivo.com/ [1] Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org> Tested-by: Lance Yang <lance.yang@linux.dev> Tested-by: Xueyuan Chen <xueyuan.chen21@gmail.com> Cc: Pedro Falcato <pfalcato@suse.de> Cc: Kairui Song <kasong@tencent.com> Cc: Qi Zheng <qi.zheng@linux.dev> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: wangzicheng <wangzicheng@honor.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Lei Liu <liulei.rjpt@vivo.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Yuanchu Xie <yuanchu@google.com> Cc: Wei Xu <weixugc@google.com> Cc: Will Deacon <will@kernel.org> Cc: Kalesh Singh <kaleshsingh@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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