mm/damon/sysfs-schemes: remove unnecessary schemes existence check in damon_sysfs_sch...

mm/damon/sysfs-schemes: remove unnecessary schemes existence check in damon_sysfs_schemes_clear_regions()

Patch series "mm/damon: replace most damon_callback usages in sysfs with
new core functions".

DAMON provides damon_callback API that notifies monitoring events and
allows safe access to damon_ctx internal data.  The usage is simple.
Users register and deregister callback functions for different monitoring
events in damon_ctx.  Then the DAMON worker thread (kdamond) of the
damon_ctx calls back the registered functions on the events.

It is designed in such simple way because it was sufficient for usages of
DAMON at the early days.  We also wanted to make it flexible so that API
user code can implement any required additional features on top of
damon_callback on their demands.

As expected, more sophisticated usages have invented.  Online updates of
DAMON parameters and DAMOS auto-tuning inputs, and online retrieval of
DAMOS statistics and tried regions information are such usages.  Because
damon_callback doesn't provide any explicit synchronization mechanism, the
user ABIs for exposing such functionalities are implemented in
asynchronous ways (DAMON_RECLAIM and DAMON_LRU_SORT}), or synchronous ways
(DAMON_SYSFS) with additional synchronization mechanisms that built inside
the ABI implementation, on top of damon_callback.

So damon_callback is working as expected.  However, the additional
mechanisms built inside ABI on top of damon_callback is becoming somewhat
too big and not easy to maintain.  The additional mechanisms can be
smaller and easier to maintain when implemented inside the core logic
layer.

Introduce two new DAMON core API, namely 'damon_call()' and
'damos_walk()'.  The two functions support synchronous access to
- damon_ctx internal data including DAMON parameters and monitoring
  results, and
- DAMOS-specific data such as regions that each DAMOS action is applied,
respectively.

And replace most of damon_callback usages in DAMON sysfs interface with
the new core API functions.  damon_callback usage for online DAMON
parameters tuning is not replaced in this series, since it has specific
callback timing assumptions that require more works.

Patch sequence
==============

First two patches are fixups for simplifying the following changes.  Those
remove a unnecessary condition check and a synchronization, respectively.

Third patch implements one of the new DAMON core APIs, namely
damon_call().  Three patches replacing damon_callback usages in DAMON
sysfs interface using damon_call() follow.

Then, seventh and eighth patches introduces the other new DAMON API,
damos_walk(), and document it on the design doc.  Ninth patch replaces two
damon_callback usages in DAMON sysfs interface using damos_walk().

The tenth patch finally cleans up code that no more being used.

This patch (of 10):

damon_sysfs_schemes_clear_regions() skips removing the scheme tried region
directories only if the matching scheme is still ongoing.  It is
unnecessary check, since what users want is just removing the entire
region directories.  Remove the unnecessary check.

Link: https://lkml.kernel.org/r/20250103174400.54890-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20250103174400.54890-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>