cst/cache: Add metric for in-memory trims

src/v/cloud_storage/cache_probe.cc

@@ -114,6 +114,12 @@ cache_probe::cache_probe() {
                     "Number of times could not free the expected amount of "
                     "space, indicating possible bug or configuration issue."))
                   .aggregate(aggregate_labels),
+                sm::make_counter(
+                  "in_mem_trims",
+                  [this] { return _in_mem_trims; },
+                  sm::description("Number of times we trimmed the cache using "
+                                  "the in-memory access tracker."))
+                  .aggregate(aggregate_labels),
               });
         }
 

src/v/cloud_storage/cache_probe.h

@@ -41,6 +41,7 @@ class cache_probe {
     void exhaustive_trim() { ++_exhaustive_trims; }
     void carryover_trim() { ++_carryover_trims; }
     void failed_trim() { ++_failed_trims; }
+    void in_mem_trim() { ++_in_mem_trims; }
 
 private:
     uint64_t _num_puts = 0;
@@ -58,6 +59,7 @@ class cache_probe {
     int64_t _exhaustive_trims{0};
     int64_t _carryover_trims{0};
     int64_t _failed_trims{0};
+    int64_t _in_mem_trims{0};
 
     metrics::internal_metric_groups _metrics;
     metrics::public_metric_groups _public_metrics;

src/v/cloud_storage/cache_service.cc

@@ -390,6 +390,7 @@ ss::future<> cache::trim(
     auto trim_result = co_await do_trim(
       tracker_lru_entries, size_to_delete, objects_to_delete);
 
+    probe.in_mem_trim();
     vlog(
       cst_log.debug,
       "in-memory trim result: deleted size: {}, deleted count: {}",