[0/8] efficiently expose damos action tried regions information

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(-)