diff -aur a/src/mds/PurgeQueue.cc b/src/mds/PurgeQueue.cc
--- a/src/mds/PurgeQueue.cc	2020-03-24 04:47:45.000000000 +1100
+++ b/src/mds/PurgeQueue.cc	2020-04-09 12:32:04.974889731 +1000
@@ -501,7 +501,7 @@
 
   in_flight[expire_to] = item;
   logger->set(l_pq_executing, in_flight.size());
-  files_high_water = std::max(files_high_water, in_flight.size());
+  files_high_water = std::max(files_high_water, (uint64_t)in_flight.size());
   logger->set(l_pq_executing_high_water, files_high_water);
   auto ops = _calculate_ops(item);
   ops_in_flight += ops;
@@ -579,7 +579,7 @@
     logger->set(l_pq_executing_ops_high_water, ops_high_water);
     in_flight.erase(expire_to);
     logger->set(l_pq_executing, in_flight.size());
-    files_high_water = std::max(files_high_water, in_flight.size());
+    files_high_water = std::max(files_high_water, (uint64_t)in_flight.size());
     logger->set(l_pq_executing_high_water, files_high_water);
     return;
   }
@@ -651,7 +651,7 @@
 
   in_flight.erase(iter);
   logger->set(l_pq_executing, in_flight.size());
-  files_high_water = std::max(files_high_water, in_flight.size());
+  files_high_water = std::max(files_high_water, (uint64_t)in_flight.size());
   logger->set(l_pq_executing_high_water, files_high_water);
   dout(10) << "in_flight.size() now " << in_flight.size() << dendl;
 
Only in b/src/mds: PurgeQueue.cc.orig