Hi, Yuanchu,

Yuanchu Xie yuanchu@google.com writes:

Changes from RFC v3 -> PATCH v1:

• Updated selftest to use ksft_print_msg instead of fprintf(stderr, ...) (Muhammad Usama Anjum)
• Included more detail in patch skipping pmd_young with force_scan (Huang, Ying)
• Deferred reaccess histogram as a followup
• Removed per-memcg page age interval configs for simplicity

Changes from RFC v2 -> RFC v3:

• Update to v6.8
• Added an aging kernel thread (gated behind config)
• Added basic selftests for sysfs interface files
• Track swapped out pages for reaccesses
• Refactoring and cleanup
• Dropped the virtio-balloon extension to make things manageable

Changes from RFC v1 -> RFC v2:

• Refactored the patchs into smaller pieces
• Renamed interfaces and functions from wss to wsr (Working Set Reporting)
• Fixed build errors when CONFIG_WSR is not set
• Changed working_set_num_bins to u8 for virtio-balloon
• Added support for per-NUMA node reporting for virtio-balloon

[rfc v1] https://lore.kernel.org/linux-mm/20230509185419.1088297-1-yuanchu@google.com... [rfc v2] https://lore.kernel.org/linux-mm/20230621180454.973862-1-yuanchu@google.com/ [rfc v3] https://lore.kernel.org/linux-mm/20240327213108.2384666-1-yuanchu@google.com...

This patch series provides workingset reporting of user pages in lruvecs, of which coldness can be tracked by accessed bits and fd references. However, the concept of workingset applies generically to all types of memory, which could be kernel slab caches, discardable userspace caches (databases), or CXL.mem. Therefore, data sources might come from slab shrinkers, device drivers, or the userspace. IMO, the kernel should provide a set of workingset interfaces that should be generic enough to accommodate the various use cases, and be extensible to potential future use cases. The current proposed interfaces are not sufficient in that regard, but I would like to start somewhere, solicit feedback, and iterate.

Use cases

Job scheduling On overcommitted hosts, workingset information allows the job scheduler to right-size each job and land more jobs on the same host or NUMA node, and in the case of a job with increasing workingset, policy decisions can be made to migrate other jobs off the host/NUMA node, or oom-kill the misbehaving job. If the job shape is very different from the machine shape, knowing the workingset per-node can also help inform page allocation policies.

Proactive reclaim Workingset information allows the a container manager to proactively reclaim memory while not impacting a job's performance. While PSI may provide a reactive measure of when a proactive reclaim has reclaimed too much, workingset reporting allows the policy to be more accurate and flexible.

Ballooning (similar to proactive reclaim) While this patch series does not extend the virtio-balloon device, balloon policies benefit from workingset to more precisely determine the size of the memory balloon. On desktops/laptops/mobile devices where memory is scarce and overcommitted, the balloon sizing in multiple VMs running on the same device can be orchestrated with workingset reports from each one.

Promotion/Demotion Similar to proactive reclaim, a workingset report enables demotion to a slower tier of memory. For promotion, the workingset report interfaces need to be extended to report hotness and gather hotness information from the devices[1].

[1] https://www.opencompute.org/documents/ocp-cms-hotness-tracking-requirements-...

This mechanism can also provide a way to control the pages ping-pong caused by promotion and demotion. If different methods are used for promotion and demotion, some pages may be migrated between the fast and slow memory back and forth. Because there's no connection between promotion side and demotion side. For example, if we use NUMA balancing based promotion and MGLRU based demotion.

If we use workingset reporting on the fast memory nodes, then we can establish the connection between demotion and promotion with it. For example, the promotion hot pages threshold (determined as accessed every N seconds) should be set to make 80% of the fast memory pages pass the threshold. This can be calculated with the workingset reporting statistics.

Sysfs and Cgroup Interfaces

The interfaces are detailed in the patches that introduce them. The main idea here is we break down the workingset per-node per-memcg into time intervals (ms), e.g.

1000 anon=137368 file=24530 20000 anon=34342 file=0 30000 anon=353232 file=333608 40000 anon=407198 file=206052 9223372036854775807 anon=4925624 file=892892

I realize this does not generalize well to hotness information, but I lack the intuition for an abstraction that presents hotness in a useful way. Please advise.

Implementation

Currently, the reporting of user pages is based off of MGLRU, and therefore requires CONFIG_LRU_GEN=y. We would benefit from more MGLRU generations for a more fine-grained workingset report. I will make the generation count configurable in the next version. The workingset reporting mechanism is gated behind CONFIG_WORKINGSET_REPORT, and the aging thread is behind CONFIG_WORKINGSET_REPORT_AGING.

Yuanchu Xie (7): mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true mm: aggregate working set information into histograms mm: use refresh interval to rate-limit workingset report aggregation mm: report workingset during memory pressure driven scanning mm: extend working set reporting to memcgs mm: add kernel aging thread for workingset reporting selftest: test system-wide workingset reporting

drivers/base/node.c | 6 + include/linux/memcontrol.h | 5 + include/linux/mmzone.h | 9 + include/linux/workingset_report.h | 97 ++++ mm/Kconfig | 15 + mm/Makefile | 2 + mm/internal.h | 17 + mm/memcontrol.c | 184 +++++- mm/mm_init.c | 2 + mm/mmzone.c | 2 + mm/vmscan.c | 85 ++- mm/workingset_report.c | 545 ++++++++++++++++++ mm/workingset_report_aging.c | 127 ++++ tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 3 + .../testing/selftests/mm/workingset_report.c | 317 ++++++++++ .../testing/selftests/mm/workingset_report.h | 39 ++ .../selftests/mm/workingset_report_test.c | 332 +++++++++++ 18 files changed, 1786 insertions(+), 2 deletions(-) create mode 100644 include/linux/workingset_report.h create mode 100644 mm/workingset_report.c create mode 100644 mm/workingset_report_aging.c create mode 100644 tools/testing/selftests/mm/workingset_report.c create mode 100644 tools/testing/selftests/mm/workingset_report.h create mode 100644 tools/testing/selftests/mm/workingset_report_test.c

-- Best Regards, Huang, Ying