mirror of
https://github.com/torvalds/linux.git
synced 2026-07-29 18:51:21 +02:00
Linux kernel source tree
Patch series "mm/vmscan: add tracepoint and reason for kswapd_failures
reset", v4.
Currently, kswapd_failures is reset in multiple places (kswapd,
direct reclaim, PCP freeing, memory-tiers), but there's no way to
trace when and why it was reset, making it difficult to debug
memory reclaim issues.
This patch:
1. Introduce kswapd_clear_hopeless() as a wrapper function to
centralize kswapd_failures reset logic.
2. Introduce kswapd_test_hopeless() to encapsulate hopeless node
checks, replacing all open-coded kswapd_failures comparisons.
3. Add kswapd_clear_hopeless_reason enum to distinguish reset sources:
- KSWAPD_CLEAR_HOPELESS_KSWAPD: reset from kswapd context
- KSWAPD_CLEAR_HOPELESS_DIRECT: reset from direct reclaim
- KSWAPD_CLEAR_HOPELESS_PCP: reset from PCP page freeing
- KSWAPD_CLEAR_HOPELESS_OTHER: reset from other paths
4. Add tracepoints for better observability:
- mm_vmscan_kswapd_clear_hopeless: traces each reset with reason
- mm_vmscan_kswapd_reclaim_fail: traces each kswapd reclaim failure
Test results:
$ trace-cmd record -e vmscan:mm_vmscan_kswapd_clear_hopeless -e vmscan:mm_vmscan_kswapd_reclaim_fail
$ # generate memory pressure
$ trace-cmd report
cpus=4
kswapd0-71 [000] 27.216563: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=1
kswapd0-71 [000] 27.217169: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=2
kswapd0-71 [000] 27.217764: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=3
kswapd0-71 [000] 27.218353: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=4
kswapd0-71 [000] 27.218993: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=5
kswapd0-71 [000] 27.219744: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=6
kswapd0-71 [000] 27.220488: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=7
kswapd0-71 [000] 27.221206: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=8
kswapd0-71 [000] 27.221806: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=9
kswapd0-71 [000] 27.222634: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=10
kswapd0-71 [000] 27.223286: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=11
kswapd0-71 [000] 27.223894: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=12
kswapd0-71 [000] 27.224712: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=13
kswapd0-71 [000] 27.225424: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=14
kswapd0-71 [000] 27.226082: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=15
kswapd0-71 [000] 27.226810: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=16
kswapd1-72 [002] 27.386869: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=1
kswapd1-72 [002] 27.387435: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=2
kswapd1-72 [002] 27.388016: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=3
kswapd1-72 [002] 27.388586: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=4
kswapd1-72 [002] 27.389155: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=5
kswapd1-72 [002] 27.389723: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=6
kswapd1-72 [002] 27.390292: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=7
kswapd1-72 [002] 27.392364: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=8
kswapd1-72 [002] 27.392934: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=9
kswapd1-72 [002] 27.393504: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=10
kswapd1-72 [002] 27.394073: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=11
kswapd1-72 [002] 27.394899: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=12
kswapd1-72 [002] 27.395472: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=13
kswapd1-72 [002] 27.396055: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=14
kswapd1-72 [002] 27.396628: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=15
kswapd1-72 [002] 27.397199: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=16
kworker/u18:0-40 [002] 27.410151: mm_vmscan_kswapd_clear_hopeless: nid=0 reason=DIRECT
kswapd0-71 [000] 27.439454: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=1
kswapd0-71 [000] 27.440048: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=2
kswapd0-71 [000] 27.440634: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=3
kswapd0-71 [000] 27.441211: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=4
kswapd0-71 [000] 27.441787: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=5
kswapd0-71 [000] 27.442363: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=6
kswapd0-71 [000] 27.443030: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=7
kswapd0-71 [000] 27.443725: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=8
kswapd0-71 [000] 27.444315: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=9
kswapd0-71 [000] 27.444898: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=10
kswapd0-71 [000] 27.445476: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=11
kswapd0-71 [000] 27.446053: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=12
kswapd0-71 [000] 27.446646: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=13
kswapd0-71 [000] 27.447230: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=14
kswapd0-71 [000] 27.447812: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=15
kswapd0-71 [000] 27.448391: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=16
ann-423 [003] 28.028285: mm_vmscan_kswapd_clear_hopeless: nid=0 reason=PCP
This patch (of 2):
When kswapd fails to reclaim memory, kswapd_failures is incremented. Once
it reaches MAX_RECLAIM_RETRIES, kswapd stops running to avoid futile
reclaim attempts. However, any successful direct reclaim unconditionally
resets kswapd_failures to 0, which can cause problems.
We observed an issue in production on a multi-NUMA system where a process
allocated large amounts of anonymous pages on a single NUMA node, causing
its watermark to drop below high and evicting most file pages:
$ numastat -m
Per-node system memory usage (in MBs):
Node 0 Node 1 Total
--------------- --------------- ---------------
MemTotal 128222.19 127983.91 256206.11
MemFree 1414.48 1432.80 2847.29
MemUsed 126807.71 126551.11 252358.82
SwapCached 0.00 0.00 0.00
Active 29017.91 25554.57 54572.48
Inactive 92749.06 95377.00 188126.06
Active(anon) 28998.96 23356.47 52355.43
Inactive(anon) 92685.27 87466.11 180151.39
Active(file) 18.95 2198.10 2217.05
Inactive(file) 63.79 7910.89 7974.68
With swap disabled, only file pages can be reclaimed. When kswapd is
woken (e.g., via wake_all_kswapds()), it runs continuously but cannot
raise free memory above the high watermark since reclaimable file pages
are insufficient. Normally, kswapd would eventually stop after
kswapd_failures reaches MAX_RECLAIM_RETRIES.
However, containers on this machine have memory.high set in their cgroup.
Business processes continuously trigger the high limit, causing frequent
direct reclaim that keeps resetting kswapd_failures to 0. This prevents
kswapd from ever stopping.
The key insight is that direct reclaim triggered by cgroup memory.high
performs aggressive scanning to throttle the allocating process. With
sufficiently aggressive scanning, even hot pages will eventually be
reclaimed, making direct reclaim "successful" at freeing some memory.
However, this success does not mean the node has reached a balanced state
- the freed memory may still be insufficient to bring free pages above the
high watermark. Unconditionally resetting kswapd_failures in this case
keeps kswapd alive indefinitely.
The result is that kswapd runs endlessly. Unlike direct reclaim which
only reclaims from the allocating cgroup, kswapd scans the entire node's
memory. This causes hot file pages from all workloads on the node to be
evicted, not just those from the cgroup triggering memory.high. These
pages constantly refault, generating sustained heavy IO READ pressure
across the entire system.
Fix this by only resetting kswapd_failures when the node is actually
balanced. This allows both kswapd and direct reclaim to clear
kswapd_failures upon successful reclaim, but only when the reclaim
actually resolves the memory pressure (i.e., the node becomes balanced).
Link: https://lkml.kernel.org/r/20260120024402.387576-1-jiayuan.chen@linux.dev
Link: https://lkml.kernel.org/r/20260120024402.387576-2-jiayuan.chen@linux.dev
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
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: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 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 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