1 files changed, 51 insertions, 0 deletions
diff --git a/lib/gitlab/memory/watchdog/monitor/heap_fragmentation.rb b/lib/gitlab/memory/watchdog/monitor/heap_fragmentation.rb
new file mode 100644
index 00000000000..7748c19c6d8
--- /dev/null
+++ b/lib/gitlab/memory/watchdog/monitor/heap_fragmentation.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Memory
+    class Watchdog
+      module Monitor
+        # A monitor that observes Ruby heap fragmentation and calls
+        # memory_violation_callback when the Ruby heap has been fragmented for an extended
+        # period of time.
+        #
+        # See Gitlab::Metrics::Memory for how heap fragmentation is defined.
+        class HeapFragmentation
+          attr_reader :max_heap_fragmentation
+
+          # max_heap_fragmentation:
+          #   The degree to which the Ruby heap is allowed to be fragmented. Range [0,1].
+          def initialize(max_heap_fragmentation:)
+            @max_heap_fragmentation = max_heap_fragmentation
+            init_frag_limit_metrics
+          end
+
+          def call
+            heap_fragmentation = Gitlab::Metrics::Memory.gc_heap_fragmentation
+
+            return { threshold_violated: false, payload: {} } unless heap_fragmentation > max_heap_fragmentation
+
+            { threshold_violated: true, payload: payload(heap_fragmentation) }
+          end
+
+          private
+
+          def payload(heap_fragmentation)
+            {
+              message: 'heap fragmentation limit exceeded',
+              memwd_cur_heap_frag: heap_fragmentation,
+              memwd_max_heap_frag: max_heap_fragmentation
+            }
+          end
+
+          def init_frag_limit_metrics
+            heap_frag_limit = Gitlab::Metrics.gauge(
+              :gitlab_memwd_heap_frag_limit,
+              'The configured limit for how fragmented the Ruby heap is allowed to be'
+            )
+            heap_frag_limit.set({}, max_heap_fragmentation)
+          end
+        end
+      end
+    end
+  end
+end