Use MAP_POPULATE for our bbolt mmaps (hashicorp#13573)

* Use MAP_POPULATE for our bbolt mmaps, assuming the files fit in memory.  This should improve startup times when freelist sync is disabled.

changelog/13573.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+storage/raft: On linux, use map_populate for bolt files to improve startup time.
+```

physical/raft/bolt_32bit_test.go

@@ -32,7 +32,7 @@ func Test_BoltOptions(t *testing.T) {
 				os.Setenv(key, tc.env)
 			}
 
-			o := boltOptions()
+			o := boltOptions("")
 
 			if o.InitialMmapSize != tc.expectedSize {
 				t.Errorf("expected InitialMmapSize to be %d but it was %d", tc.expectedSize, o.InitialMmapSize)

physical/raft/bolt_64bit_test.go

@@ -32,7 +32,7 @@ func Test_BoltOptions(t *testing.T) {
 				os.Setenv(key, tc.env)
 			}
 
-			o := boltOptions()
+			o := boltOptions("")
 
 			if o.InitialMmapSize != tc.expectedSize {
 				t.Errorf("expected InitialMmapSize to be %d but it was %d", tc.expectedSize, o.InitialMmapSize)

physical/raft/bolt_linux.go

@@ -0,0 +1,36 @@
+package raft
+
+import (
+	"context"
+	"os"
+
+	"github.com/shirou/gopsutil/mem"
+	"golang.org/x/sys/unix"
+)
+
+func init() {
+	getMmapFlags = getMmapFlagsLinux
+}
+
+func getMmapFlagsLinux(dbPath string) int {
+	if os.Getenv("VAULT_RAFT_DISABLE_MAP_POPULATE") != "" {
+		return 0
+	}
+	stat, err := os.Stat(dbPath)
+	if err != nil {
+		return 0
+	}
+	size := stat.Size()
+
+	v, err := mem.VirtualMemoryWithContext(context.Background())
+	if err != nil {
+		return 0
+	}
+
+	// We won't worry about swap, since we already tell people not to use it.
+	if v.Total > uint64(size) {
+		return unix.MAP_POPULATE
+	}
+
+	return 0
+}

physical/raft/fsm.go

@@ -168,7 +168,7 @@ func (f *FSM) openDBFile(dbPath string) error {
 		}
 	}
 
-	opts := boltOptions()
+	opts := boltOptions(dbPath)
 	start := time.Now()
 	boltDB, err := bolt.Open(dbPath, 0o600, opts)
 	if err != nil {

physical/raft/raft.go

@@ -40,6 +40,8 @@ const EnvVaultRaftNodeID = "VAULT_RAFT_NODE_ID"
 // EnvVaultRaftPath is used to fetch the path where Raft data is stored from the environment.
 const EnvVaultRaftPath = "VAULT_RAFT_PATH"
 
+var getMmapFlags = func(string) int { return 0 }
+
 // Verify RaftBackend satisfies the correct interfaces
 var (
 	_ physical.Backend       = (*RaftBackend)(nil)
@@ -364,9 +366,10 @@ func NewRaftBackend(conf map[string]string, logger log.Logger) (physical.Backend
 		}
 
 		// Create the backend raft store for logs and stable storage.
-		opts := boltOptions()
+		dbPath := filepath.Join(path, "raft.db")
+		opts := boltOptions(dbPath)
 		raftOptions := raftboltdb.Options{
-			Path:        filepath.Join(path, "raft.db"),
+			Path:        dbPath,
 			BoltOptions: opts,
 		}
 		store, err := raftboltdb.New(raftOptions)
@@ -1649,11 +1652,12 @@ func (s sealer) Open(ctx context.Context, ct []byte) ([]byte, error) {
 
 // boltOptions returns a bolt.Options struct, suitable for passing to
 // bolt.Open(), pre-configured with all of our preferred defaults.
-func boltOptions() *bolt.Options {
+func boltOptions(path string) *bolt.Options {
 	o := &bolt.Options{
 		Timeout:        1 * time.Second,
 		FreelistType:   bolt.FreelistMapType,
 		NoFreelistSync: true,
+		MmapFlags:      getMmapFlags(path),
 	}
 
 	if os.Getenv("VAULT_RAFT_FREELIST_TYPE") == "array" {