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b=uWwqW/IbIQSxR7WAexf6dNLzEPriLBPWkOrtKaDXrSodU/jR6bqYHU8zlYqx4RdVY dlRMCGJnEOhReOrQ7fqcOIuPn0BznEU1upLOicsUjU4B/bQU8UaKuRRdgjq4rFimqx NAEHPX8pAFkBm/spKRN4zNHuftXB3JRW8jKBdLKGHpoWfiIQX+ZhC1t8itmmpiYnU8 lYc12eVK5Qy7f6pdagHUg/Xot4AROneCKD6oDTm06er/UonsxejPtaBPAPdHCGPSEG dw3PFAyapZv1gCPaXkGskrYeyWM/dYbG/fF/0ObhuNde3Fj9Q13VUmBLoUilTYl4qV GWHjYUg6e5zKw== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , Jonathan Corbet , damon@lists.linux.dev, kernel-team@meta.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 4/4] Docs/admin-guide/mm/damon: add DAMON_STAT usage document Date: Wed, 4 Jun 2025 11:31:27 -0700 Message-Id: <20250604183127.13968-5-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250604183127.13968-1-sj@kernel.org> References: <20250604183127.13968-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: ddbq6chxncj9ytdm75bykrrd5nn8odki X-Rspamd-Queue-Id: 49AEE1C0016 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749061897-139152 X-HE-Meta: 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 h712GEBJ v4ri18fsNixKgIa8OhOCginX00j3sPcpesjLlrIDZ7PnoJdjgB06PTsBBKwEhO4Ibx1StTQL9Pb3nIClhwNHJ1lzw9n37u9k0spIPzLPqs5/b9zc2oCfzVXlO3QdQLU/XJsWlQgEhXa9Ez2K6Xulu3KOb2Pb8rcBKsX1hnR0aHyHu1aTXWnJJfUiHeIeQfs2P2qdQR/E4IBD1gtfnbs1L7OrlygYlh3iMtTve84MrF1jdcuD2znjKv1IGdP9A/LcQAwqEL/c95wntL5MgrN+Oq9wwJQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Document DAMON_STAT usage and add a link to it on DAMON admin-guide page. Signed-off-by: SeongJae Park --- Documentation/admin-guide/mm/damon/index.rst | 1 + Documentation/admin-guide/mm/damon/stat.rst | 69 ++++++++++++++++++++ 2 files changed, 70 insertions(+) create mode 100644 Documentation/admin-guide/mm/damon/stat.rst diff --git a/Documentation/admin-guide/mm/damon/index.rst b/Documentation/admin-guide/mm/damon/index.rst index bc7e976120e0..3ce3164480c7 100644 --- a/Documentation/admin-guide/mm/damon/index.rst +++ b/Documentation/admin-guide/mm/damon/index.rst @@ -14,3 +14,4 @@ access monitoring and access-aware system operations. usage reclaim lru_sort + stat diff --git a/Documentation/admin-guide/mm/damon/stat.rst b/Documentation/admin-guide/mm/damon/stat.rst new file mode 100644 index 000000000000..4c517c2c219a --- /dev/null +++ b/Documentation/admin-guide/mm/damon/stat.rst @@ -0,0 +1,69 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +Data Access Monitoring Results Stat +=================================== + +Data Access Monitoring Results Stat (DAMON_STAT) is a static kernel module that +is aimed to be used for simple access pattern monitoring. It monitors accesses +on the system's entire physical memory using DAMON, and provides simplified +access monitoring results statistics, namely idle time percentiles and +estimated memory bandwidth. + +Monitoring Accuracy and Overhead +================================ + +DAMON_STAT uses monitoring intervals :ref:`auto-tuning +` to make its accuracy high and +overhead minimum. It auto-tunes the intervals aiming 4 % of observable access +events to be captured in each snapshot, while limiting the resulting sampling +events to be 5 milliseconds in minimum and 10 seconds in maximum. On a few +production server systems, it resulted in consuming only 0.x % single CPU time, +while capturing reasonable quality of access patterns. + +Interface: Module Parameters +============================ + +To use this feature, you should first ensure your system is running on a kernel +that is built with ``CONFIG_DAMON_STAT=y``. The feature can be enabled by +default at build time, by setting ``CONFIG_DAMON_STAT_ENABLED_DEFAULT`` true. + +To let sysadmins enable or disable it at boot and/or runtime, and read the +monitoring results, DAMON_STAT provides module parameters. Following +sections are descriptions of the parameters. + +enabled +------- + +Enable or disable DAMON_STAT. + +You can enable DAMON_STAT by setting the value of this parameter as ``Y``. +Setting it as ``N`` disables DAMON_STAT. The default value is set by +``CONFIG_DAMON_STAT_ENABLED_DEFAULT`` build config option. + +estimated_memory_bandwidth +-------------------------- + +Estimated memory bandwidth consumption (bytes per second) of the system. + +DAMON_STAT reads observed access events on the current DAMON results snapshot +and converts it to memory bandwidth consumption estimation in bytes per second. +The resulting metric is exposed to user via this read-only parameter. Because +DAMON uses sampling, this is only an estimation of the access intensity rather +than accurate memory bandwidth. + +memory_idle_ms_percentiles +-------------------------- + +Per-byte idle time (milliseconds) percentiles of the system. + +DAMON_STAT calculates how long each byte of the memory was not accessed until +now (idle time), based on the current DAMON results snapshot. If DAMON found a +region of access frequency (nr_accesses) larger than zero, every byte of the +region gets zero idle time. If a region has zero access frequency +(nr_accesses), how long the region was keeping the zero access frequency (age) +becomes the idle time of every byte of the region. Then, DAMON_STAT exposes +the percentiles of the idle time values via this read-only parameter. Reading +the parameter returns 101 idle time values in milliseconds, separated by comma. +Each value represents 0-th, 1st, 2nd, 3rd, ..., 99th and 100th percentile idle +times. -- 2.39.5