fix: remove persistence layer for metacache store in memory (#11538)

store the cache in-memory instead of disks to avoid large
write amplifications for list heavy workloads, store in
memory instead and let it auto expire.

cmd/erasure.go

@@ -30,6 +30,7 @@ import (
 	"github.com/minio/minio/pkg/color"
 	"github.com/minio/minio/pkg/dsync"
 	"github.com/minio/minio/pkg/madmin"
+	"github.com/minio/minio/pkg/objcache"
 	"github.com/minio/minio/pkg/sync/errgroup"
 )
 
@@ -70,6 +71,9 @@ type erasureObjects struct {
 	// Byte pools used for temporary i/o buffers.
 	bp *bpool.BytePoolCap
 
+	// holds current list cache.
+	metaCache *objcache.Cache
+
 	mrfOpCh chan partialOperation
 }