[RFC PATCH 03/27] mm/damon/core: introduce damon_submit_report()

[SJ Park <sj@kernel.org>]

Implement and expose a new DAMON API function for submitting a data
attribute report.  Any kernel component in any context including NMI
context can use it to report their finding of data attribute information
for a given memory.

The function copies the content of the report into the DAMON-internal
report queue.  The copy is done in a ring buffer-like manner, without
being blocked for consumption.  As a result, the queue keeps the latest
reports up to its capacity.

Use simple CAS-based try-locking.  If any parallel submission is
detected, simply forgive the submission.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 5c32ddebf4625..ca0135c6f6700 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1189,6 +1189,8 @@ int damon_kdamond_pid(struct damon_ctx *ctx);
 int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
 int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
 
+int damon_submit_report(struct damon_report *report);
+
 int damon_set_region_system_rams_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end,
 				unsigned long addr_unit,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3f87a7eec442e..06b85d00e38d9 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2353,6 +2353,36 @@ struct damon_report_queue {
 
 struct damon_report_queue damon_report_queue;
 
+/**
+ * damon_submit_report() - Enqueue a given report to DAMON internal buffer.
+ * @report:	The report to enqueue.
+ *
+ * This function can be called from any context including the NMI context.
+ */
+int damon_submit_report(struct damon_report *report)
+{
+	struct damon_report_queue *queue;
+	int lock_old_val;
+	unsigned int tail;
+
+	queue = &damon_report_queue;
+	report->jiffies = jiffies;
+	lock_old_val = atomic_cmpxchg(&queue->lock, 0, 1);
+	if (lock_old_val)
+		return -EBUSY;
+
+	tail = queue->tail;
+	if (tail == queue->size)
+		tail = 0;
+	queue->reports[tail] = *report;
+	queue->tail++;
+	if (queue->nr_reports < queue->size)
+		queue->nr_reports++;
+	/* cmpxchg is known to be faster than xchg */
+	atomic_cmpxchg(&queue->lock, 1, 0);
+	return 0;
+}
+
 /*
  * Reset the aggregated monitoring results ('nr_accesses' of each region).
  */
-- 
2.47.3