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[23.116.43.216]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-69e069b0ea8sm1442784eaf.12.2026.05.29.09.56.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 May 2026 09:56:58 -0700 (PDT) From: Ravi Jonnalagadda To: sj@kernel.org, akinobu.mita@gmail.com, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: akpm@linux-foundation.org, corbet@lwn.net, bijan311@gmail.com, ajayjoshi@micron.com, honggyu.kim@sk.com, yunjeong.mun@sk.com, ravis.opensrc@gmail.com Subject: [RFC PATCH 0/6] mm/damon: hardware-sampled access reports Date: Fri, 29 May 2026 09:56:34 -0700 Message-ID: <20260529165640.820-1-ravis.opensrc@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This series introduces a vendor and PMU-agnostic substrate inside DAMON that consumes hardware-sampled access reports through the standard perf-event interface. Userspace selects the PMU through sysfs (raw type/config knobs), driving either Intel PEBS L3-miss sampling or AMD IBS Op sampling. Why a unified perf-event substrate Earlier hardware-sampled access-monitoring proposal [1] took an AMD IBS specific module path backend, owning its own probe configuration, sysfs knobs, and lifecycle. SeongJae Park has previously highlighted the advantage of Akinobu Mita's perf-event proposal [2]: let DAMON register kernel-counter perf events and consume samples from any sampling PMU that perf core knows about. This series builds on that direction with the changes we needed to run it cross-vendor: - a per-CPU lockless ring between the NMI sample handler and the kdamond drain, - per-CPU events that follow CPU hotplug cleanly, - events fire only while the monitor is running -- created disabled, armed when kdamond starts, disarmed and drained when it stops, - all-or-nothing init across CPUs: a partial-CPU create failure rolls the whole event back rather than leaving silent gaps, - safe handling of vendor sample-validity flags so a stale or unpopulated address is never mistaken for a valid sample. What the series adds Patch 1 introduces the substrate's data types: a per-event configuration struct and a per-context list to hang them on. A CONFIG_PERF_EVENTS=n build folds to no-op stubs. Patch 2 exposes those types through sysfs. Each entry maps to one perf event and lets userspace pick the PMU and how to sample it: the raw PMU type/config, addressing flags, and period or frequency. The defaults are tuned for Intel PEBS; userspace overrides them for other PMUs. Patch 3 wires the sysfs apply path so configured events get attached to the running monitoring context. Patch 4 is the core of the series. It replaces the mutex-protected report queue with a per-CPU lockless ring fed from NMI by the perf overflow handler and drained once per sample tick by the kdamond. Drained reports are matched to monitored regions by binary search over a per-tick snapshot. The patch also wires the per-event lifecycle into kdamond: events arm when the monitor starts, disarm and drain when it stops, roll back cleanly when per-CPU init fails on some CPUs, and a second context that asks for the substrate while it is in use is rejected with -EBUSY. Patch 5 is the perf-event backend. Two stateless overflow handlers (one vaddr-keyed, one paddr-keyed) are picked at event creation time and submit samples into the per-CPU ring. Vendor-specific sample validity is honored at this layer. Patch 6 adds a tracepoint at every node_eligible_mem_bp quota-goal evaluation so userspace can watch goal convergence without polling sysfs. Userspace setup model Userspace selects the sampling PMU by pointing the perf event's `type` / `config` at it, and chooses the scheme topology that suits the address space the PMU reports on. No module load or unload step is involved; `echo on > state` arms the substrate, `echo off > state` disarms it. Two configurations were used for validation. Configuration A: AMD IBS Op, paddr ops, system-wide PULL+PUSH tiering IBS Op stamps samples with physical addresses, so DAMON reasons over every backing page in the system regardless of which task or guest touched it -- the substrate becomes a system-wide tiering controller. Setup (abridged; `D=/sys/kernel/mm/damon/admin/kdamonds/0`): echo 1 > /sys/kernel/mm/damon/admin/kdamonds/nr_kdamonds echo 1 > $D/contexts/nr_contexts echo paddr > $D/contexts/0/operations # Two regions, one per NUMA node (DRAM + CXL). PA ranges # are derived per host from /proc/iomem; omitted here. echo 1 > $D/contexts/0/targets/nr_targets echo 2 > $D/contexts/0/targets/0/regions/nr_regions echo > $D/contexts/0/targets/0/regions/0/start echo > $D/contexts/0/targets/0/regions/0/end echo > $D/contexts/0/targets/0/regions/1/start echo > $D/contexts/0/targets/0/regions/1/end # IBS Op event, period-based, paddr-stamped: PE=$D/contexts/0/monitoring_attrs/sample/perf_events echo 1 > $PE/nr_perf_events echo $(cat /sys/bus/event_source/devices/ibs_op/type) > $PE/0/type echo 0 > $PE/0/config echo 1 > $PE/0/sample_phys_addr echo 0 > $PE/0/freq echo 262144 > $PE/0/sample_period echo 0 > $PE/0/exclude_kernel echo 0 > $PE/0/exclude_hv # PULL scheme: migrate_hot toward DRAM, gated on # node_eligible_mem_bp(nid=DRAM) goal target_value=TARGET_BP. # addr filter restricts source to the CXL range. # PUSH scheme: migrate_hot toward CXL, gated on # node_eligible_mem_bp(nid=CXL) target_value=10000-TARGET_BP. # addr filter restricts source to the DRAM range. # Both schemes are migrate_hot; they converge from opposite # directions on the same hot working set. echo on > $D/state Userspace tunes the steady-state DRAM:CXL split by writing the goal `target_value`s; DAMON's quota autotuner drives migration intensity to match. Workload: a QEMU/KVM guest pinned to one NUMA node, running 32 multichase multiload threads each touching a 4 GiB working set (~128 GiB aggregate) with the memcpy-libc kernel. The guest sees a flat single-NUMA layout and has no direct view of the host's tiering topology, yet its hot pages are migrated to DRAM and cold pages pushed to CXL by host-side DAMON acting on IBS-stamped physical addresses -- the application inside the guest benefits from tiering it never had to be aware of. Validated on AMD Turin (132-CPU EPYC). The configuration converged to its target ratio in seconds and remained stable for 7+ hours continuously, with no perf core auto-throttle and no measurable drift in the achieved interleave ratio. Configuration B: Intel PEBS L3-miss, vaddr ops, per-PID weighted-dest PEBS reports vaddr samples in the context of the running task. DAMON's vaddr ops monitors a specific PID. Setup (abridged): echo 1 > /sys/kernel/mm/damon/admin/kdamonds/nr_kdamonds echo 1 > $D/contexts/nr_contexts echo vaddr > $D/contexts/0/operations echo 1 > $D/contexts/0/targets/nr_targets echo $PID > $D/contexts/0/targets/0/pid_target echo 0 > $D/contexts/0/targets/0/regions/nr_regions # PEBS MEM_LOAD_RETIRED.L3_MISS, frequency-based, vaddr-stamped: echo 1 > $PE/nr_perf_events echo 4 > $PE/0/type # PERF_TYPE_RAW echo 0x20d1 > $PE/0/config # umask=0x20 event=0xd1 echo 0 > $PE/0/sample_phys_addr echo 1 > $PE/0/freq echo 5003 > $PE/0/sample_freq echo 2 > $PE/0/precise_ip echo 1 > $PE/0/wakeup_events # Single migrate_hot scheme with two weighted destinations # (DRAM + CXL). Userspace tunes the steady-state interleave by # writing dests/{0,1}/weight. echo on > $D/state Workload: 32 multichase multiload threads with a 4 GiB working set each (~128 GiB aggregate) running directly on the host, monitored by DAMON via the multiload PID. Validated on Intel Granite Rapids (144-CPU). Convergence is fast and the system is stable. [1] https://lore.kernel.org/linux-mm/20260516223439.4033-1-ravis.opensrc@gmail.com/ [2] https://lore.kernel.org/20260423004211.7037-1-akinobu.mita@gmail.com Ravi Jonnalagadda (6): mm/damon: add struct damon_perf_event{,_attr} and per-ctx perf_events list mm/damon/sysfs-sample: expose perf_events configuration via sysfs mm/damon/sysfs: install perf_events on apply mm/damon/core: per-CPU SPSC ring drain and damon_perf_event lifecycle mm/damon/vaddr: implement perf-event access check mm/damon: add damos_node_eligible_mem_bp tracepoint include/linux/damon.h | 80 +++++ include/trace/events/damon.h | 49 +++ mm/damon/core.c | 403 ++++++++++++++++++++---- mm/damon/ops-common.h | 39 +++ mm/damon/sysfs-common.h | 6 + mm/damon/sysfs-sample.c | 579 +++++++++++++++++++++++++++++++++++ mm/damon/sysfs.c | 3 + mm/damon/vaddr.c | 267 ++++++++++++++++ 8 files changed, 1370 insertions(+), 56 deletions(-) base-commit: 4c8ad15abf15eb480d3ad85f902001e35465ef18 -- 2.43.0