[RFC PATCH 13/27] mm/damon/core: introduce damon_report_exist()

[SJ Park <sj@kernel.org>]

Implement and expose a new DAMON API function for searching data
attribute reports from the report queue.  The purpose is to let
operation sets use it for supporting the REPORT_MADE type probe filters.

The caller can specify the type, associated memory address range, and
the creation time range of reports to search.

The function uses CAS-based try-locking for the mutual-exclusive
synchronization.  If any parallel access to the queue is detected, it
forgives searching.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h |  3 +++
 mm/damon/core.c       | 46 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index cce7d344c585b..0e43b669dfc49 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1193,6 +1193,9 @@ 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);
+bool damon_report_exist(enum damon_report_type report_type,
+		struct damon_addr_range *addr_range,
+		unsigned long jiffies_old);
 
 int damon_set_region_system_rams_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end,
diff --git a/mm/damon/core.c b/mm/damon/core.c
index c02c7fbc1d864..c60a6504d0a15 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2386,6 +2386,52 @@ int damon_submit_report(struct damon_report *report)
 	return 0;
 }
 
+/**
+ * damon_report_exist() - Find if a report of a given condition exists.
+ *
+ * @report_type:	Type of the report.
+ * @addr_range:		Address range of the report.
+ * @jiffies_old:	Oldest jiffies to find the report for.
+ *
+ * Returns true if the report is found, false otherwise.
+ */
+bool damon_report_exist(enum damon_report_type report_type,
+		struct damon_addr_range *addr_range, unsigned long jiffies_old)
+{
+	struct damon_report_queue *queue;
+	int lock_old_val;
+	unsigned int idx, nr_read;
+	struct damon_report *report;
+	bool found = false;
+
+	queue = &damon_report_queue;
+	lock_old_val = atomic_cmpxchg(&queue->lock, 0, 1);
+
+	if (lock_old_val)
+		return false;
+	idx = queue->tail;
+	for (nr_read = 0; nr_read < queue->nr_reports; nr_read++) {
+		report = &queue->reports[idx];
+		if (idx)
+			idx--;
+		else
+			idx = queue->size - 1;
+
+		if (time_before(report->jiffies, jiffies_old))
+			break;
+		if (report->type != report_type)
+			continue;
+		if (addr_range->end <= report->addr_range.start ||
+				report->addr_range.end <= addr_range->start)
+			continue;
+		found = true;
+		break;
+	}
+
+	atomic_cmpxchg(&queue->lock, 1, 0);
+	return found;
+}
+
 /*
  * Reset the aggregated monitoring results ('nr_accesses' of each region).
  */
-- 
2.47.3