DAMON: add priority-based scheme application control

This patchset introduces a priority mechanism for DAMON's scheme
application, allowing users to specify the relative importance of
monitored processes.  The changes ensure that higher-priority targets
receive more frequent memory management operations while maintaining
fairness across all monitored processes.

The first patch modifies kdamond_apply_schemes to implement
priority-based scheduling, where targets are processed in proportion to
their assigned priority values.  For example, a target with priority 50
will be serviced 50 times for every 30 times a target with priority 30
is processed.

The second patch adds a sysfs interface (priority under each target's
directory) to dynamically configure these priorities at runtime. This
enables fine-grained control over DAMON's behavior, making it more
adaptable to performance-sensitive workloads.

Together, these changes provide better flexibility for users who need
differentiated memory management policies across different processes
while maintaining backward compatibility with existing setups.

You may want to verify this feature using the following testing
procedure:

 # git clone -b v2 https://github.com/lienze/damo.git
 # cd damo
 # ./damo start --target_pid $(pidof <target1>) --priority 50 \
 --target_pid $(pidof <target2>) --priority 30 --damos_action \
 pageout --damos_age 5s 5s

Enze Li (2):
  mm/damon/core: introduce priority concept for DAMON
  mm/damon/sysfs: add priority support for DAMOS targets

 include/linux/damon.h |  2 +
 mm/damon/core.c       | 91 ++++++++++++++++++++++++++++++++++++++++++-
 mm/damon/sysfs.c      | 28 +++++++++++++
 3 files changed, 119 insertions(+), 2 deletions(-)

-- 
2.51.0