XL/erasure: Reset dataBlocks to reduce the memory usage. (#1749)

Fixes #1748

erasure-readfile.go

@@ -147,6 +147,9 @@ func (e erasure) ReadFile(volume, path string, startOffset int64, totalSize int6
 				return
 			}
 
+			// Reset dataBlocks to relenquish memory.
+			dataBlocks = nil
+
 			// Reset offset to '0' to read rest of the blocks.
 			startOffset = int64(0)
 

erasure-utils.go

@@ -17,8 +17,7 @@
 package main
 
 // getDataBlocks - fetches the data block only part of the input encoded blocks.
-func getDataBlocks(enBlocks [][]byte, dataBlocks int, curBlockSize int) []byte {
+func getDataBlocks(enBlocks [][]byte, dataBlocks int, curBlockSize int) (data []byte) {
-	var data []byte
 	for _, block := range enBlocks[:dataBlocks] {
 		data = append(data, block...)
 	}