mm/damon/core: clarify damon_set_attrs() usages

damon_set_attrs() is called for multiple purposes from multiple places.
Calling it in an unsafe context can make DAMON internal state polluted and
results in unexpected behaviors.  Clarify when it is safe, and where it is
being called.

Link: https://lkml.kernel.org/r/20260307195356.203753-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: wang lian <lianux.mm@gmail.com>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index db44294745e6e01a272b90730d5627909c64038d..2d2332f3d3773cec67dd5b8566869b074eeac0ea 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -751,8 +751,16 @@ static bool damon_valid_intervals_goal(struct damon_attrs *attrs)
  * @ctx:               monitoring context
  * @attrs:             monitoring attributes
  *
- * This function should be called while the kdamond is not running, an access
- * check results aggregation is not ongoing (e.g., from damon_call().
+ * This function updates monitoring results and next monitoring/damos operation
+ * schedules.  Because those are periodically updated by kdamond, this should
+ * be called from a safe contexts.  Such contexts include damon_ctx setup time
+ * while the kdamond is not yet started, and inside of kdamond_fn().
+ *
+ * In detail, all DAMON API callers directly call this function for initial
+ * setup of damon_ctx before calling damon_start().  Some of the API callers
+ * also indirectly call this function via damon_call() -> damon_commit() for
+ * online parameters updates.  Finally, kdamond_fn() itself use this for
+ * applying auto-tuned monitoring intervals.
  *
  * Every time interval is in micro-seconds.
  *