feat: splitstore: access warmupepoch atomically instead of locking

blockstore/splitstore/splitstore.go

@@ -164,7 +164,7 @@ type SplitStore struct {
 	path string
 
 	mx          sync.Mutex
-	warmupEpoch abi.ChainEpoch // protected by mx
+	warmupEpoch int64          // atomically accessed
 	baseEpoch   abi.ChainEpoch // protected by compaction lock
 	pruneEpoch  abi.ChainEpoch // protected by compaction lock
 
@@ -684,9 +684,7 @@ func (s *SplitStore) View(ctx context.Context, cid cid.Cid, cb func([]byte) erro
 }
 
 func (s *SplitStore) isWarm() bool {
-	s.mx.Lock()
-	defer s.mx.Unlock()
-	return s.warmupEpoch > 0
+	return atomic.LoadInt64(&s.warmupEpoch) > 0
 }
 
 // State tracking
@@ -757,7 +755,7 @@ func (s *SplitStore) Start(chain ChainAccessor, us stmgr.UpgradeSchedule) error
 	bs, err = s.ds.Get(s.ctx, warmupEpochKey)
 	switch err {
 	case nil:
-		s.warmupEpoch = bytesToEpoch(bs)
+		atomic.StoreInt64(&s.warmupEpoch, bytesToInt64(bs))
 
 	case dstore.ErrNotFound:
 		warmup = true
@@ -791,7 +789,7 @@ func (s *SplitStore) Start(chain ChainAccessor, us stmgr.UpgradeSchedule) error
 		return xerrors.Errorf("error loading compaction index: %w", err)
 	}
 
-	log.Infow("starting splitstore", "baseEpoch", s.baseEpoch, "warmupEpoch", s.warmupEpoch)
+	log.Infow("starting splitstore", "baseEpoch", s.baseEpoch, "warmupEpoch", atomic.LoadInt64(&s.warmupEpoch))
 
 	if warmup {
 		err = s.warmup(curTs)

blockstore/splitstore/splitstore_check.go

@@ -145,7 +145,7 @@ func (s *SplitStore) doCheck(curTs *types.TipSet) error {
 func (s *SplitStore) Info() map[string]interface{} {
 	info := make(map[string]interface{})
 	info["base epoch"] = s.baseEpoch
-	info["warmup epoch"] = s.warmupEpoch
+	info["warmup epoch"] = atomic.LoadInt64(&s.warmupEpoch)
 	info["compactions"] = s.compactionIndex
 	info["prunes"] = s.pruneIndex
 	info["compacting"] = s.compacting == 1

blockstore/splitstore/splitstore_warmup.go

@@ -137,7 +137,7 @@ func (s *SplitStore) doWarmup(curTs *types.TipSet) error {
 		return xerrors.Errorf("error saving warm up epoch: %w", err)
 	}
 	s.mx.Lock()
-	s.warmupEpoch = epoch
+	atomic.StoreInt64(&s.warmupEpoch, int64(epoch))
 	s.mx.Unlock()
 
 	// also save the compactionIndex, as this is used as an indicator of warmup for upgraded nodes