vfs: reduce memory usage by re-ordering commonly used structures

vfs/file.go

@@ -39,19 +39,19 @@ type File struct {
 	inode uint64 // inode number - read only
 	size  int64  // size of file - read and written with atomic int64 - must be 64 bit aligned
 
+	muRW sync.Mutex // synchronize RWFileHandle.openPending(), RWFileHandle.close() and File.Remove
+
 	mu               sync.RWMutex                    // protects the following
 	d                *Dir                            // parent directory
 	dPath            string                          // path of parent directory. NB dir rename means all Files are flushed
 	o                fs.Object                       // NB o may be nil if file is being written
 	leaf             string                          // leaf name of the object
 	writers          []Handle                        // writers for this file
-	nwriters         int32                           // len(writers) which is read/updated with atomic
 	pendingModTime   time.Time                       // will be applied once o becomes available, i.e. after file was written
 	pendingRenameFun func(ctx context.Context) error // will be run/renamed after all writers close
-	appendMode       bool                            // file was opened with O_APPEND
 	sys              atomic.Value                    // user defined info to be attached here
-
-	muRW sync.Mutex // synchronize RWFileHandle.openPending(), RWFileHandle.close() and File.Remove
+	nwriters         int32                           // len(writers) which is read/updated with atomic
+	appendMode       bool                            // file was opened with O_APPEND
 }
 
 // newFile creates a new File

vfs/read.go

@@ -21,18 +21,18 @@ type ReadFileHandle struct {
 	done        func(ctx context.Context, err error)
 	mu          sync.Mutex
 	cond        sync.Cond // cond lock for out of sequence reads
-	closed      bool       // set if handle has been closed
 	r           *accounting.Account
-	readCalled  bool  // set if read has been called
 	size        int64 // size of the object (0 for unknown length)
 	offset      int64 // offset of read of o
 	roffset     int64 // offset of Read() calls
-	noSeek      bool
-	sizeUnknown bool // set if size of source is not known
 	file        *File
 	hash        *hash.MultiHasher
-	opened      bool
 	remote      string
+	closed      bool // set if handle has been closed
+	readCalled  bool // set if read has been called
+	noSeek      bool
+	sizeUnknown bool // set if size of source is not known
+	opened      bool
 }
 
 // Check interfaces

vfs/vfscache/item.go

@@ -63,10 +63,10 @@ type Item struct {
 	downloaders     *downloaders.Downloaders // a record of the downloaders in action - may be nil
 	o               fs.Object                // object we are caching - may be nil
 	fd              *os.File                 // handle we are using to read and write to the file
-	modified        bool                     // set if the file has been modified since the last Open
 	info            Info                     // info about the file to persist to backing store
 	writeBackID     writeback.Handle         // id of any writebacks in progress
 	pendingAccesses int                      // number of threads - cache reset not allowed if not zero
+	modified        bool                     // set if the file has been modified since the last Open
 	beingReset      bool                     // cache cleaner is resetting the cache file, access not allowed
 }
 

vfs/write.go

@@ -16,16 +16,16 @@ type WriteFileHandle struct {
 	baseHandle
 	mu          sync.Mutex
 	cond        sync.Cond // cond lock for out of sequence writes
-	closed      bool       // set if handle has been closed
 	remote      string
 	pipeWriter  *io.PipeWriter
 	o           fs.Object
 	result      chan error
 	file        *File
-	writeCalled bool // set the first time Write() is called
 	offset      int64
-	opened      bool
 	flags       int
+	closed      bool // set if handle has been closed
+	writeCalled bool // set the first time Write() is called
+	opened      bool
 	truncated   bool
 }