Index: lucene/src/java/org/apache/lucene/store/FSDirectory.java
===================================================================
--- lucene/src/java/org/apache/lucene/store/FSDirectory.java	(revision 37a8afc06777c7747838ba3acc9523ee5a14c16d)
+++ lucene/src/java/org/apache/lucene/store/FSDirectory.java	(revision )
@@ -319,6 +319,19 @@
     }
   }
 
+  /**
+   * Sets the rate limiter to be used to limit (approx) MB/sec allowed
+   * by all IO performed when merging. Pass null to have no limit.
+   *
+   * <p>Passing an instance of rate limiter compared to setting it using
+   * {@link #setMaxMergeWriteMBPerSec(Double)} allows to use the same limiter
+   * instance across several directories globally limiting IO when merging
+   * across them.
+   */
+  public synchronized void setMaxMergeWriteLimiter(RateLimiter mergeWriteRateLimiter) {
+    this.mergeWriteRateLimiter = mergeWriteRateLimiter;
+  }
+
   /** See {@link #setMaxMergeWriteMBPerSec}.
    *
    * @lucene.experimental */