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44467bbb7e
Patch series "efficiently expose damos action tried regions information". DAMON users can retrieve the monitoring results via 'after_aggregation' callbacks if the user is using the kernel API, or 'damon_aggregated' tracepoint if the user is in the user space. Those are useful if full monitoring results are necessary. However, if the user has interest in only a snapshot of the results for some regions having specific access pattern, the interfaces could be inefficient. For example, some users only want to know which memory regions are not accessed for more than a specific time at the moment. Also, some DAMOS users would want to know exactly to what memory regions the schemes' actions tried to be applied, for a debugging or a tuning. As DAMOS has its internal mechanism for quota and regions prioritization, the users would need to simulate DAMOS' mechanism against the monitoring results. That's unnecessarily complex. This patchset implements DAMON kernel API callbacks and sysfs directory for efficient exposure of the information for the use cases. The new callback will be called for each region when a DAMOS action is gonna tried to be applied to it. The sysfs directory will be called 'tried_regions' and placed under each scheme sysfs directory. Users can write a special keyworkd, 'update_schemes_regions', to the 'state' file of a kdamond sysfs directory. Then, DAMON sysfs interface will fill the directory with the information of regions that corresponding scheme action was tried to be applied for next one aggregation interval. Patches Sequence ---------------- The first one (patch 1) implements the callback for the kernel space users. Following two patches (patches 2 and 3) implements sysfs directories for the information and its sub directories. Two patches (patches 4 and 5) for implementing the special keywords for filling the data to and cleaning up the directories follow. Patch 6 adds a selftest for the new sysfs directory. Finally, two patches (patches 7 and 8) document the new feature in the administrator guide and the ABI document. This patch (of 8): Getting DAMON monitoring results of only specific access pattern (e.g., getting address ranges of memory that not accessed at all for two minutes) can be useful for efficient monitoring of the system. The information can also be helpful for deep level investigation of DAMON-based operation schemes. For that, users need to record (in case of the user space users) or iterate (in case of the kernel space users) full monitoring results and filter it out for the specific access pattern. In case of the DAMOS investigation, users will even need to simulate DAMOS' quota and prioritization mechanisms. It's inefficient and complex. Add a new DAMON callback that will be called before each scheme is applied to each region. DAMON kernel API users will be able to do the query-like monitoring results collection, or DAMOS investigation in an efficient and simple way using it. Commits for providing the capability to the user space users will follow. Link: https://lkml.kernel.org/r/20221101220328.95765-1-sj@kernel.org Link: https://lkml.kernel.org/r/20221101220328.95765-2-sj@kernel.org Signed-off-by: SeongJae Park <sj@kernel.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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