Changes from RFC (https://lore.kernel.org/damon/20221019001317.104270-1-sj@kernel.org/): - Split out cleanup/refactoring parts[1]

[1] https://lore.kernel.org/damon/20221026225943.100429-1-sj@kernel.org/

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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.

Assembled Tree --------------

This patchset is based on the latest mm-unstable tree[1]. Assembled tree is also available at the damon/next tree[2].

[1] https://git.kernel.org/akpm/mm/h/mm-unstable [2] https://git.kernel.org/sj/h/damon/next

SeongJae Park (8): mm/damon/core: add a callback for scheme target regions check mm/damon/sysfs-schemes: implement schemes/tried_regions directory mm/damon/sysfs-schemes: implement scheme region directory mm/damon/sysfs: implement DAMOS tried regions update command mm/damon/sysfs-schemes: implement DAMOS-tried regions clear command tools/selftets/damon/sysfs: test tried_regions directory existence Docs/admin-guide/mm/damon/usage: document schemes/<s>/tried_regions sysfs directory Docs/ABI/damon: document 'schemes/<s>/tried_regions' sysfs directory

.../ABI/testing/sysfs-kernel-mm-damon | 32 +++ Documentation/admin-guide/mm/damon/usage.rst | 45 ++- include/linux/damon.h | 5 + mm/damon/core.c | 6 +- mm/damon/sysfs-common.h | 10 + mm/damon/sysfs-schemes.c | 261 ++++++++++++++++++ mm/damon/sysfs.c | 77 +++++- tools/testing/selftests/damon/sysfs.sh | 7 + 8 files changed, 437 insertions(+), 6 deletions(-)