]> git.proxmox.com Git - ceph.git/blobdiff - ceph/src/mds/Beacon.cc
import quincy beta 17.1.0
[ceph.git] / ceph / src / mds / Beacon.cc
index e94390f65bf4fbb834ade342b9bcfbc85547058f..766e4c5d26711e7a55b00eafebea1dc223e91bd0 100644 (file)
@@ -19,7 +19,6 @@
 #include "include/stringify.h"
 #include "include/util.h"
 
-#include "messages/MMDSBeacon.h"
 #include "mon/MonClient.h"
 #include "mds/MDLog.h"
 #include "mds/MDSRank.h"
 
 #include "Beacon.h"
 
+#include <chrono>
+
 #define dout_context g_ceph_context
 #define dout_subsys ceph_subsys_mds
 #undef dout_prefix
 #define dout_prefix *_dout << "mds.beacon." << name << ' '
 
+using std::map;
+using std::string;
 
-Beacon::Beacon(CephContext *cct_, MonClient *monc_, boost::string_view name_) :
-  Dispatcher(cct_), lock("Beacon"), monc(monc_), timer(g_ceph_context, lock),
-  name(name_), standby_for_rank(MDS_RANK_NONE),
-  standby_for_fscid(FS_CLUSTER_ID_NONE), want_state(MDSMap::STATE_BOOT),
-  awaiting_seq(-1)
-{
-  last_seq = 0;
-  was_laggy = false;
+using namespace std::chrono_literals;
 
-  epoch = 0;
+Beacon::Beacon(CephContext *cct, MonClient *monc, std::string_view name)
+  :
+    Dispatcher(cct),
+    beacon_interval(g_conf()->mds_beacon_interval),
+    monc(monc),
+    name(name),
+    compat(MDSMap::get_compat_set_all())
+{
 }
 
-
 Beacon::~Beacon()
 {
+  shutdown();
 }
 
+void Beacon::shutdown()
+{
+  std::unique_lock<std::mutex> lock(mutex);
+  if (!finished) {
+    finished = true;
+    lock.unlock();
+    if (sender.joinable())
+      sender.join();
+  }
+}
 
-void Beacon::init(MDSMap const *mdsmap)
+void Beacon::init(const MDSMap &mdsmap)
 {
-  Mutex::Locker l(lock);
-  assert(mdsmap != NULL);
+  std::unique_lock lock(mutex);
 
   _notify_mdsmap(mdsmap);
-  standby_for_rank = mds_rank_t(g_conf->mds_standby_for_rank);
-  standby_for_name = g_conf->mds_standby_for_name;
-  standby_for_fscid = fs_cluster_id_t(g_conf->mds_standby_for_fscid);
-  standby_replay = g_conf->mds_standby_replay;
 
-  // Spawn threads and start messaging
-  timer.init();
-  _send();
+  sender = std::thread([this]() {
+    std::unique_lock<std::mutex> lock(mutex);
+    std::condition_variable c; // no one wakes us
+    while (!finished) {
+      auto now = clock::now();
+      auto since = std::chrono::duration<double>(now-last_send).count();
+      auto interval = beacon_interval;
+      if (since >= interval*.90) {
+        if (!_send()) {
+          interval = 0.5; /* 500ms */
+        }
+      } else {
+        interval -= since;
+      }
+      dout(20) << "sender thread waiting interval " << interval << "s" << dendl;
+      c.wait_for(lock, interval*1s);
+    }
+  });
 }
 
-
-void Beacon::shutdown()
+bool Beacon::ms_can_fast_dispatch2(const cref_t<Message>& m) const
 {
-  Mutex::Locker l(lock);
-  if (sender) {
-    timer.cancel_event(sender);
-    sender = NULL;
-  }
-  timer.shutdown();
+  return m->get_type() == MSG_MDS_BEACON;
 }
 
+void Beacon::ms_fast_dispatch2(const ref_t<Message>& m)
+{
+  bool handled = ms_dispatch2(m);
+  ceph_assert(handled);
+}
 
-bool Beacon::ms_dispatch(Message *m)
+bool Beacon::ms_dispatch2(const ref_t<Message>& m)
 {
   if (m->get_type() == MSG_MDS_BEACON) {
     if (m->get_connection()->get_peer_type() == CEPH_ENTITY_TYPE_MON) {
-      handle_mds_beacon(static_cast<MMDSBeacon*>(m));
+      handle_mds_beacon(ref_cast<MMDSBeacon>(m));
     }
     return true;
   }
@@ -98,196 +120,149 @@ bool Beacon::ms_dispatch(Message *m)
  *
  * This function puts the passed message before returning
  */
-void Beacon::handle_mds_beacon(MMDSBeacon *m)
+void Beacon::handle_mds_beacon(const cref_t<MMDSBeacon> &m)
 {
-  Mutex::Locker l(lock);
-  assert(m != NULL);
+  std::unique_lock lock(mutex);
 
   version_t seq = m->get_seq();
 
   // update lab
-  if (seq_stamp.count(seq)) {
-    utime_t now = ceph_clock_now();
-    if (seq_stamp[seq] > last_acked_stamp) {
-      last_acked_stamp = seq_stamp[seq];
-      utime_t rtt = now - last_acked_stamp;
-
-      dout(10) << "handle_mds_beacon " << ceph_mds_state_name(m->get_state())
-              << " seq " << m->get_seq() << " rtt " << rtt << dendl;
-
-      if (was_laggy && rtt < g_conf->mds_beacon_grace) {
-       dout(0) << "handle_mds_beacon no longer laggy" << dendl;
-       was_laggy = false;
-       laggy_until = now;
-      }
-    } else {
-      // Mark myself laggy if system clock goes backwards. Hopping
-      // later beacons will clear it.
-      dout(1) << "handle_mds_beacon system clock goes backwards, "
-             << "mark myself laggy" << dendl;
-      last_acked_stamp = now - utime_t(g_conf->mds_beacon_grace + 1, 0);
-      was_laggy = true;
+  auto it = seq_stamp.find(seq);
+  if (it != seq_stamp.end()) {
+    auto now = clock::now();
+
+    last_acked_stamp = it->second;
+    auto rtt = std::chrono::duration<double>(now - last_acked_stamp).count();
+
+    dout(5) << "received beacon reply " << ceph_mds_state_name(m->get_state()) << " seq " << m->get_seq() << " rtt " << rtt << dendl;
+
+    if (laggy && rtt < g_conf()->mds_beacon_grace) {
+      dout(0) << " MDS is no longer laggy" << dendl;
+      laggy = false;
+      last_laggy = now;
     }
 
     // clean up seq_stamp map
-    while (!seq_stamp.empty() &&
-          seq_stamp.begin()->first <= seq)
-      seq_stamp.erase(seq_stamp.begin());
+    seq_stamp.erase(seq_stamp.begin(), ++it);
 
     // Wake a waiter up if present
-    if (awaiting_seq == seq) {
-      waiting_cond.Signal();
-    }
+    cvar.notify_all();
   } else {
-    dout(10) << "handle_mds_beacon " << ceph_mds_state_name(m->get_state())
-            << " seq " << m->get_seq() << " dne" << dendl;
+    dout(1) << "discarding unexpected beacon reply " << ceph_mds_state_name(m->get_state())
+           << " seq " << m->get_seq() << " dne" << dendl;
   }
-  m->put();
 }
 
 
 void Beacon::send()
 {
-  Mutex::Locker l(lock);
+  std::unique_lock lock(mutex);
   _send();
 }
 
 
 void Beacon::send_and_wait(const double duration)
 {
-  Mutex::Locker l(lock);
+  std::unique_lock lock(mutex);
   _send();
-  awaiting_seq = last_seq;
+  auto awaiting_seq = last_seq;
   dout(20) << __func__ << ": awaiting " << awaiting_seq
            << " for up to " << duration << "s" << dendl;
 
-  utime_t timeout;
-  timeout.set_from_double(ceph_clock_now() + duration);
-  while ((!seq_stamp.empty() && seq_stamp.begin()->first <= awaiting_seq)
-         && ceph_clock_now() < timeout) {
-    waiting_cond.WaitUntil(lock, timeout);
+  auto start = clock::now();
+  while (!seq_stamp.empty() && seq_stamp.begin()->first <= awaiting_seq) {
+    auto now = clock::now();
+    auto s = duration*.95-std::chrono::duration<double>(now-start).count();
+    if (s < 0) break;
+    cvar.wait_for(lock, s*1s);
   }
-
-  awaiting_seq = -1;
 }
 
 
 /**
  * Call periodically, or when you have updated the desired state
  */
-void Beacon::_send()
+bool Beacon::_send()
 {
-  if (sender) {
-    timer.cancel_event(sender);
-  }
-  sender = timer.add_event_after(
-    g_conf->mds_beacon_interval,
-    new FunctionContext([this](int) {
-       assert(lock.is_locked_by_me());
-       sender = nullptr;
-       _send();
-      }));
+  auto now = clock::now();
+  auto since = std::chrono::duration<double>(now-last_acked_stamp).count();
 
   if (!cct->get_heartbeat_map()->is_healthy()) {
     /* If anything isn't progressing, let avoid sending a beacon so that
      * the MDS will consider us laggy */
-    dout(1) << __func__ << " skipping beacon, heartbeat map not healthy" << dendl;
-    return;
+    dout(0) << "Skipping beacon heartbeat to monitors (last acked " << since << "s ago); MDS internal heartbeat is not healthy!" << dendl;
+    return false;
   }
 
   ++last_seq;
-  dout(10) << __func__ << " " << ceph_mds_state_name(want_state)
-          << " seq " << last_seq
-          << dendl;
+  dout(5) << "Sending beacon " << ceph_mds_state_name(want_state) << " seq " << last_seq << dendl;
 
-  seq_stamp[last_seq] = ceph_clock_now();
+  seq_stamp[last_seq] = now;
 
-  assert(want_state != MDSMap::STATE_NULL);
+  ceph_assert(want_state != MDSMap::STATE_NULL);
   
-  MMDSBeacon *beacon = new MMDSBeacon(
+  auto beacon = make_message<MMDSBeacon>(
       monc->get_fsid(), mds_gid_t(monc->get_global_id()),
       name,
       epoch,
       want_state,
       last_seq,
       CEPH_FEATURES_SUPPORTED_DEFAULT);
-
-  beacon->set_standby_for_rank(standby_for_rank);
-  beacon->set_standby_for_name(standby_for_name);
-  beacon->set_standby_for_fscid(standby_for_fscid);
-  beacon->set_standby_replay(standby_replay);
   beacon->set_health(health);
   beacon->set_compat(compat);
+  beacon->set_fs(g_conf().get_val<std::string>("mds_join_fs"));
   // piggyback the sys info on beacon msg
   if (want_state == MDSMap::STATE_BOOT) {
     map<string, string> sys_info;
     collect_sys_info(&sys_info, cct);
-    sys_info["addr"] = stringify(monc->get_myaddr());
+    sys_info["addr"] = stringify(monc->get_myaddrs());
     beacon->set_sys_info(sys_info);
   }
-  monc->send_mon_message(beacon);
+  monc->send_mon_message(beacon.detach());
+  last_send = now;
+  return true;
 }
 
 /**
  * Call this when there is a new MDSMap available
  */
-void Beacon::notify_mdsmap(MDSMap const *mdsmap)
+void Beacon::notify_mdsmap(const MDSMap &mdsmap)
 {
-  Mutex::Locker l(lock);
-  assert(mdsmap != NULL);
+  std::unique_lock lock(mutex);
 
   _notify_mdsmap(mdsmap);
 }
 
-void Beacon::_notify_mdsmap(MDSMap const *mdsmap)
+void Beacon::_notify_mdsmap(const MDSMap &mdsmap)
 {
-  assert(mdsmap != NULL);
-  assert(mdsmap->get_epoch() >= epoch);
+  ceph_assert(mdsmap.get_epoch() >= epoch);
 
-  if (mdsmap->get_epoch() != epoch) {
-    epoch = mdsmap->get_epoch();
-    compat = get_mdsmap_compat_set_default();
-    compat.merge(mdsmap->compat);
+  if (mdsmap.get_epoch() >= epoch) {
+    epoch = mdsmap.get_epoch();
   }
 }
 
 
 bool Beacon::is_laggy()
 {
-  Mutex::Locker l(lock);
-
-  if (last_acked_stamp == utime_t())
-    return false;
-
-  utime_t now = ceph_clock_now();
-  utime_t since = now - last_acked_stamp;
-  if (since > g_conf->mds_beacon_grace) {
-    dout(5) << "is_laggy " << since << " > " << g_conf->mds_beacon_grace
-           << " since last acked beacon" << dendl;
-    was_laggy = true;
-    if (since > (g_conf->mds_beacon_grace*2) &&
-       now > last_mon_reconnect + g_conf->mds_beacon_interval) {
-      // maybe it's not us?
-      dout(5) << "initiating monitor reconnect; maybe we're not the slow one"
-              << dendl;
-      last_mon_reconnect = now;
-      monc->reopen_session();
+  std::unique_lock lock(mutex);
+
+  auto now = clock::now();
+  auto since = std::chrono::duration<double>(now-last_acked_stamp).count();
+  if (since > g_conf()->mds_beacon_grace) {
+    if (!laggy) {
+      dout(1) << "MDS connection to Monitors appears to be laggy; " << since
+             << "s since last acked beacon" << dendl;
     }
+    laggy = true;
     return true;
   }
   return false;
 }
 
-utime_t Beacon::get_laggy_until() const
-{
-  Mutex::Locker l(lock);
-
-  return laggy_until;
-}
-
-void Beacon::set_want_state(MDSMap const *mdsmap, MDSMap::DaemonState const newstate)
+void Beacon::set_want_state(const MDSMap &mdsmap, MDSMap::DaemonState newstate)
 {
-  Mutex::Locker l(lock);
+  std::unique_lock lock(mutex);
 
   // Update mdsmap epoch atomically with updating want_state, so that when
   // we send a beacon with the new want state it has the latest epoch, and
@@ -297,7 +272,7 @@ void Beacon::set_want_state(MDSMap const *mdsmap, MDSMap::DaemonState const news
   _notify_mdsmap(mdsmap);
 
   if (want_state != newstate) {
-    dout(10) << __func__ << ": "
+    dout(5) << __func__ << ": "
       << ceph_mds_state_name(want_state) << " -> "
       << ceph_mds_state_name(newstate) << dendl;
     want_state = newstate;
@@ -312,14 +287,14 @@ void Beacon::set_want_state(MDSMap const *mdsmap, MDSMap::DaemonState const news
  */
 void Beacon::notify_health(MDSRank const *mds)
 {
-  Mutex::Locker l(lock);
+  std::unique_lock lock(mutex);
   if (!mds) {
     // No MDS rank held
     return;
   }
 
   // I'm going to touch this MDS, so it must be locked
-  assert(mds->mds_lock.is_locked_by_me());
+  ceph_assert(ceph_mutex_is_locked_by_me(mds->mds_lock));
 
   health.metrics.clear();
 
@@ -331,16 +306,16 @@ void Beacon::notify_health(MDSRank const *mds)
   }
 
   // Detect MDS_HEALTH_TRIM condition
-  // Arbitrary factor of 2, indicates MDS is not trimming promptly
+  // Indicates MDS is not trimming promptly
   {
-    if (mds->mdlog->get_num_segments() > (size_t)(g_conf->mds_log_max_segments * 2)) {
-      std::ostringstream oss;
-      oss << "Behind on trimming (" << mds->mdlog->get_num_segments()
-        << "/" << g_conf->mds_log_max_segments << ")";
+    if (mds->mdlog->get_num_segments() > (size_t)(g_conf()->mds_log_max_segments * g_conf().get_val<double>("mds_log_warn_factor"))) {
+      CachedStackStringStream css;
+      *css << "Behind on trimming (" << mds->mdlog->get_num_segments()
+        << "/" << g_conf()->mds_log_max_segments << ")";
 
-      MDSHealthMetric m(MDS_HEALTH_TRIM, HEALTH_WARN, oss.str());
+      MDSHealthMetric m(MDS_HEALTH_TRIM, HEALTH_WARN, css->strv());
       m.metadata["num_segments"] = stringify(mds->mdlog->get_num_segments());
-      m.metadata["max_segments"] = stringify(g_conf->mds_log_max_segments);
+      m.metadata["max_segments"] = stringify(g_conf()->mds_log_max_segments);
       health.metrics.push_back(m);
     }
   }
@@ -348,40 +323,38 @@ void Beacon::notify_health(MDSRank const *mds)
   // Detect clients failing to respond to modifications to capabilities in
   // CLIENT_CAPS messages.
   {
-    std::list<client_t> late_clients;
-    mds->locker->get_late_revoking_clients(&late_clients);
-    std::list<MDSHealthMetric> late_cap_metrics;
-
-    for (std::list<client_t>::iterator i = late_clients.begin(); i != late_clients.end(); ++i) {
+    auto&& late_clients = mds->locker->get_late_revoking_clients(mds->mdsmap->get_session_timeout());
+    std::vector<MDSHealthMetric> late_cap_metrics;
 
+    for (const auto& client : late_clients) {
       // client_t is equivalent to session.info.inst.name.num
       // Construct an entity_name_t to lookup into SessionMap
-      entity_name_t ename(CEPH_ENTITY_TYPE_CLIENT, i->v);
+      entity_name_t ename(CEPH_ENTITY_TYPE_CLIENT, client.v);
       Session const *s = mds->sessionmap.get_session(ename);
       if (s == NULL) {
         // Shouldn't happen, but not worth crashing if it does as this is
         // just health-reporting code.
-        derr << "Client ID without session: " << i->v << dendl;
+        derr << "Client ID without session: " << client.v << dendl;
         continue;
       }
 
-      std::ostringstream oss;
-      oss << "Client " << s->get_human_name() << " failing to respond to capability release";
-      MDSHealthMetric m(MDS_HEALTH_CLIENT_LATE_RELEASE, HEALTH_WARN, oss.str());
-      m.metadata["client_id"] = stringify(i->v);
-      late_cap_metrics.push_back(m);
+      CachedStackStringStream css;
+      *css << "Client " << s->get_human_name() << " failing to respond to capability release";
+      MDSHealthMetric m(MDS_HEALTH_CLIENT_LATE_RELEASE, HEALTH_WARN, css->strv());
+      m.metadata["client_id"] = stringify(client.v);
+      late_cap_metrics.emplace_back(std::move(m));
     }
 
-    if (late_cap_metrics.size() <= (size_t)g_conf->mds_health_summarize_threshold) {
-      health.metrics.splice(health.metrics.end(), late_cap_metrics);
+    if (late_cap_metrics.size() <= (size_t)g_conf()->mds_health_summarize_threshold) {
+      auto&& m = late_cap_metrics;
+      health.metrics.insert(std::end(health.metrics), std::cbegin(m), std::cend(m));
     } else {
-      std::ostringstream oss;
-      oss << "Many clients (" << late_cap_metrics.size()
+      CachedStackStringStream css;
+      *css << "Many clients (" << late_cap_metrics.size()
           << ") failing to respond to capability release";
-      MDSHealthMetric m(MDS_HEALTH_CLIENT_LATE_RELEASE_MANY, HEALTH_WARN, oss.str());
+      MDSHealthMetric m(MDS_HEALTH_CLIENT_LATE_RELEASE_MANY, HEALTH_WARN, css->strv());
       m.metadata["client_count"] = stringify(late_cap_metrics.size());
-      health.metrics.push_back(m);
-      late_cap_metrics.clear();
+      health.metrics.push_back(std::move(m));
     }
   }
 
@@ -390,66 +363,61 @@ void Beacon::notify_health(MDSRank const *mds)
   //
   // Detect clients failing to advance their old_client_tid
   {
-    set<Session*> sessions;
+    std::set<Session*> sessions;
     mds->sessionmap.get_client_session_set(sessions);
 
-    utime_t cutoff = ceph_clock_now();
-    cutoff -= g_conf->mds_recall_state_timeout;
-    utime_t last_recall = mds->mdcache->last_recall_state;
-
-    std::list<MDSHealthMetric> late_recall_metrics;
-    std::list<MDSHealthMetric> large_completed_requests_metrics;
-    for (set<Session*>::iterator i = sessions.begin(); i != sessions.end(); ++i) {
-      Session *session = *i;
-      if (!session->recalled_at.is_zero()) {
-        dout(20) << "Session servicing RECALL " << session->info.inst
-          << ": " << session->recalled_at << " " << session->recall_release_count
-          << "/" << session->recall_count << dendl;
-       if (last_recall < cutoff || session->last_recall_sent < last_recall) {
-         dout(20) << "  no longer recall" << dendl;
-         session->clear_recalled_at();
-       } else if (session->recalled_at < cutoff) {
-          dout(20) << "  exceeded timeout " << session->recalled_at << " vs. " << cutoff << dendl;
-          std::ostringstream oss;
-         oss << "Client " << session->get_human_name() << " failing to respond to cache pressure";
-          MDSHealthMetric m(MDS_HEALTH_CLIENT_RECALL, HEALTH_WARN, oss.str());
-          m.metadata["client_id"] = stringify(session->info.inst.name.num());
-          late_recall_metrics.push_back(m);
-        } else {
-          dout(20) << "  within timeout " << session->recalled_at << " vs. " << cutoff << dendl;
-        }
+    const auto min_caps_working_set = g_conf().get_val<uint64_t>("mds_min_caps_working_set");
+    const auto recall_warning_threshold = g_conf().get_val<Option::size_t>("mds_recall_warning_threshold");
+    const auto max_completed_requests = g_conf()->mds_max_completed_requests;
+    const auto max_completed_flushes = g_conf()->mds_max_completed_flushes;
+    std::vector<MDSHealthMetric> late_recall_metrics;
+    std::vector<MDSHealthMetric> large_completed_requests_metrics;
+    for (auto& session : sessions) {
+      const uint64_t num_caps = session->get_num_caps();
+      const uint64_t recall_caps = session->get_recall_caps();
+      if (recall_caps > recall_warning_threshold && num_caps > min_caps_working_set) {
+        dout(2) << "Session " << *session <<
+             " is not releasing caps fast enough. Recalled caps at " << recall_caps
+          << " > " << recall_warning_threshold << " (mds_recall_warning_threshold)." << dendl;
+        CachedStackStringStream css;
+        *css << "Client " << session->get_human_name() << " failing to respond to cache pressure";
+        MDSHealthMetric m(MDS_HEALTH_CLIENT_RECALL, HEALTH_WARN, css->strv());
+        m.metadata["client_id"] = stringify(session->get_client());
+        late_recall_metrics.emplace_back(std::move(m));
       }
       if ((session->get_num_trim_requests_warnings() > 0 &&
-          session->get_num_completed_requests() >= g_conf->mds_max_completed_requests) ||
+          session->get_num_completed_requests() >= max_completed_requests) ||
          (session->get_num_trim_flushes_warnings() > 0 &&
-          session->get_num_completed_flushes() >= g_conf->mds_max_completed_flushes)) {
-       std::ostringstream oss;
-       oss << "Client " << session->get_human_name() << " failing to advance its oldest client/flush tid";
-       MDSHealthMetric m(MDS_HEALTH_CLIENT_OLDEST_TID, HEALTH_WARN, oss.str());
-       m.metadata["client_id"] = stringify(session->info.inst.name.num());
-       large_completed_requests_metrics.push_back(m);
+          session->get_num_completed_flushes() >= max_completed_flushes)) {
+       CachedStackStringStream css;
+       *css << "Client " << session->get_human_name() << " failing to advance its oldest client/flush tid. ";
+       MDSHealthMetric m(MDS_HEALTH_CLIENT_OLDEST_TID, HEALTH_WARN, css->strv());
+       m.metadata["client_id"] = stringify(session->get_client());
+       large_completed_requests_metrics.emplace_back(std::move(m));
       }
     }
 
-    if (late_recall_metrics.size() <= (size_t)g_conf->mds_health_summarize_threshold) {
-      health.metrics.splice(health.metrics.end(), late_recall_metrics);
+    if (late_recall_metrics.size() <= (size_t)g_conf()->mds_health_summarize_threshold) {
+      auto&& m = late_recall_metrics;
+      health.metrics.insert(std::end(health.metrics), std::cbegin(m), std::cend(m));
     } else {
-      std::ostringstream oss;
-      oss << "Many clients (" << late_recall_metrics.size()
+      CachedStackStringStream css;
+      *css << "Many clients (" << late_recall_metrics.size()
           << ") failing to respond to cache pressure";
-      MDSHealthMetric m(MDS_HEALTH_CLIENT_RECALL_MANY, HEALTH_WARN, oss.str());
+      MDSHealthMetric m(MDS_HEALTH_CLIENT_RECALL_MANY, HEALTH_WARN, css->strv());
       m.metadata["client_count"] = stringify(late_recall_metrics.size());
       health.metrics.push_back(m);
       late_recall_metrics.clear();
     }
 
-    if (large_completed_requests_metrics.size() <= (size_t)g_conf->mds_health_summarize_threshold) {
-      health.metrics.splice(health.metrics.end(), large_completed_requests_metrics);
+    if (large_completed_requests_metrics.size() <= (size_t)g_conf()->mds_health_summarize_threshold) {
+      auto&& m = large_completed_requests_metrics;
+      health.metrics.insert(std::end(health.metrics), std::cbegin(m), std::cend(m));
     } else {
-      std::ostringstream oss;
-      oss << "Many clients (" << large_completed_requests_metrics.size()
+      CachedStackStringStream css;
+      *css << "Many clients (" << large_completed_requests_metrics.size()
        << ") failing to advance their oldest client/flush tid";
-      MDSHealthMetric m(MDS_HEALTH_CLIENT_OLDEST_TID_MANY, HEALTH_WARN, oss.str());
+      MDSHealthMetric m(MDS_HEALTH_CLIENT_OLDEST_TID_MANY, HEALTH_WARN, css->strv());
       m.metadata["client_count"] = stringify(large_completed_requests_metrics.size());
       health.metrics.push_back(m);
       large_completed_requests_metrics.clear();
@@ -459,12 +427,32 @@ void Beacon::notify_health(MDSRank const *mds)
   // Detect MDS_HEALTH_SLOW_REQUEST condition
   {
     int slow = mds->get_mds_slow_req_count();
-    dout(20) << slow << " slow request found" << dendl;
     if (slow) {
-      std::ostringstream oss;
-      oss << slow << " slow requests are blocked > " << g_conf->mds_op_complaint_time << " sec";
+      dout(20) << slow << " slow request found" << dendl;
+      CachedStackStringStream css;
+      *css << slow << " slow requests are blocked > " << g_conf()->mds_op_complaint_time << " secs";
+
+      MDSHealthMetric m(MDS_HEALTH_SLOW_REQUEST, HEALTH_WARN, css->strv());
+      health.metrics.push_back(m);
+    }
+  }
+
+  {
+    auto complaint_time = g_conf()->osd_op_complaint_time;
+    auto now = clock::now();
+    auto cutoff = now - ceph::make_timespan(complaint_time);
+
+    std::string count;
+    ceph::coarse_mono_time oldest;
+    if (MDSIOContextBase::check_ios_in_flight(cutoff, count, oldest)) {
+      dout(20) << count << " slow metadata IOs found" << dendl;
+
+      auto oldest_secs = std::chrono::duration<double>(now - oldest).count();
+      CachedStackStringStream css;
+      *css << count << " slow metadata IOs are blocked > " << complaint_time
+         << " secs, oldest blocked for " << (int64_t)oldest_secs << " secs";
 
-      MDSHealthMetric m(MDS_HEALTH_SLOW_REQUEST, HEALTH_WARN, oss.str());
+      MDSHealthMetric m(MDS_HEALTH_SLOW_METADATA_IO, HEALTH_WARN, css->strv());
       health.metrics.push_back(m);
     }
   }
@@ -478,20 +466,20 @@ void Beacon::notify_health(MDSRank const *mds)
 
   // Report if we have significantly exceeded our cache size limit
   if (mds->mdcache->cache_overfull()) {
-    std::ostringstream oss;
-    oss << "MDS cache is too large (" << bytes2str(mds->mdcache->cache_size())
+    CachedStackStringStream css;
+    *css << "MDS cache is too large (" << bytes2str(mds->mdcache->cache_size())
         << "/" << bytes2str(mds->mdcache->cache_limit_memory()) << "); "
         << mds->mdcache->num_inodes_with_caps << " inodes in use by clients, "
         << mds->mdcache->get_num_strays() << " stray files";
 
-    MDSHealthMetric m(MDS_HEALTH_CACHE_OVERSIZED, HEALTH_WARN, oss.str());
+    MDSHealthMetric m(MDS_HEALTH_CACHE_OVERSIZED, HEALTH_WARN, css->strv());
     health.metrics.push_back(m);
   }
 }
 
 MDSMap::DaemonState Beacon::get_want_state() const
 {
-  Mutex::Locker l(lock);
+  std::unique_lock lock(mutex);
   return want_state;
 }