From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1E5EB1DE8BE; Sun, 26 Apr 2026 20:52:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777236755; cv=none; b=Sr2fP4SYpBaZe3gyAjkVl2E2oupz3lIXiMKcI/0Mt2hiIGrFTpxli+XyfaqX5J4MC18maTGGTDa12U2pjFs88OsRr74SawdsLJGCmzc0nYitCX++kwwLNAmHw4iL3td3EDvyUvw+KY1EsEklxAutn1jDTdH2F9lqLqFUfk4Z8fg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777236755; c=relaxed/simple; bh=WxWvBmm0LZfVg5AjkZ36lir3AfpAPctV6FKdU/pjfLQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=nH3+FWFN3jEWNG/aCggnacYZ27qYki/Y2NhaPUrdMcGLDJmb4v1Ykh0asuelpiATjR2OJEBIUtTkdfrmWmBrIcdmpaysjwertrQy54cgOwaYDkI9JXwJPTuJ1La9wdF9h2Sb7duXNpUl1DDyxrcdMJIQR8hvWCUIDhzqIm7W9p0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NmTB/zGa; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NmTB/zGa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04C24C2BCAF; Sun, 26 Apr 2026 20:52:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777236754; bh=WxWvBmm0LZfVg5AjkZ36lir3AfpAPctV6FKdU/pjfLQ=; h=From:To:Cc:Subject:Date:From; b=NmTB/zGaPmAdpd80S+HXHEDUf0uXzdPa5Dj6ei7/vnqLPdt79eZd/q2HgAgJgmZFC l8iZ66IpFhH+3b0Ip3yp6L3o6KqGDioB7HBX+QTq/+C/1bMd1Evkj8KinUQtOFZ/lf 3Dc2EKxzRHXoxYrdZjSC+byGkLpMNCB6tuUML6Ok5qjNGevYOPpc89RRij9onvEoz+ Z1Xyc3i9v2XORNhfNfmCbA0b/c46fNbVX9VqCTlWKD+TqarI2uaMfSrDygxHaBNdHl efOket+drnaSr197jO8hhaCZ53zyIqWFZ4IxrRyq+pQ5alwBpPFB6ZFwJBEBa4MyRo KIfZYi0WhyqKQ== From: SeongJae Park To: Cc: SeongJae Park , "Liam R. Howlett" , Andrew Morton , David Hildenbrand , Jonathan Corbet , Lorenzo Stoakes , Masami Hiramatsu , Mathieu Desnoyers , Michal Hocko , Mike Rapoport , Shuah Khan , Shuah Khan , Steven Rostedt , Suren Baghdasaryan , Vlastimil Babka , damon@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: [RFC PATCH 00/19] mm/damon: introduce data attributes monitoring Date: Sun, 26 Apr 2026 13:52:01 -0700 Message-ID: <20260426205222.93895-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit TL; DR ====== Extend DAMON for monitoring general data attributes other than accesses. This is for enabling light-weight page type (e.g., belonging cgroup) aware monitoring in short term. 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 hot cgroup A 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. Eight changes for user interface (patches 9-16) 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. Patch 15 implements sysfs files for showing the per-region per-probe positive samples count, namely probe_hits. Patch 16 introduces a new tracepoint for showing the counts via tracefs. Patch 14 adds a selftest for the sysfs files. Patches 15 and 16 documents the design and usage of the new feature, respectively. Discussions =========== 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. Plan for Dropping RFC tag ========================= The user ABI for reading probe_hits is not yet convincing. It is exposed to users by a tracepoint and new sysfs file. For the tracepoint, a new one namely damon:damon_aggregated_v2 is introduced. The name is not convincing, and its internal mechanism seems to have room to be improved before dropping RFC. For the sysfs, a file under the DAMOS-tried region directory namely 'probe_hits' is added. Reading it returns four probe_hits values with ',' as a separator. With the maximum number of data probes, this should work. This can make future changes of the limit difficult. I will try to find a better way before dropping the RFC tag. Maybe 'probe_hits/' directory having files of name '0' to 'N-1' for each of user-registered 'N' data probes. I'm currently hoping to drop the RFC tag by 7.2-rc1. Future Works: Short Term ======================== This series is introducing only a single type of data attribute: anonymous page. Once this is landed, I will extend it for cgroup-belonging, so that we can do cgroup-level monitoring with low overhead. After that, I may further work on supporting all DAMOS filter types. And as demands are found, we could extend the types. 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, if it is easy to do. 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". [1] https://lore.kernel.org/20250106193401.109161-1-sj@kernel.org [2] https://lore.kernel.org/20251208062943.68824-1-sj@kernel.org/ [3] https://lore.kernel.org/20260423004211.7037-1-akinobu.mita@gmail.com SeongJae Park (19): mm/damon/core: introduce struct damon_probe mm/damon/core: embed damon_probe objects in damon_ctx mm/damon/core: introduce damon_filter mm/damon/core: commit probes mm/damon/core: introduce damon_region->probe_hits mm/damon/core: introduce damon_ops->apply_probes mm/damon/core: do data attributes monitoring mm/damon/paddr: support data attributes monitoring mm/damon/sysfs: implement probes dir mm/damon/sysfs: implement probe dir mm/damon/sysfs: implement filters directory mm/damon/sysfs: implement filter dir mm/damon/sysfs: implement filter dir files mm/damon/sysfs: setup probes on DAMON core API parameters mm/damon/sysfs-schemes: implement tried_region/probe_hits file mm/damon: trace probe_hits selftests/damon/sysfs.sh: test probes dir Docs/mm/damon/design: document data attributes monitoring Docs/admin-guide/mm/damon/usage: document data attributes monitoring Documentation/admin-guide/mm/damon/usage.rst | 44 +- Documentation/mm/damon/design.rst | 37 ++ include/linux/damon.h | 60 +++ include/trace/events/damon.h | 41 ++ mm/damon/core.c | 182 +++++++ mm/damon/paddr.c | 45 ++ mm/damon/sysfs-schemes.c | 30 ++ mm/damon/sysfs.c | 502 +++++++++++++++++++ tools/testing/selftests/damon/sysfs.sh | 48 ++ 9 files changed, 982 insertions(+), 7 deletions(-) base-commit: 8f22aa2e28454419ed2031119ad32ea4a6c9f1f1 -- 2.47.3