[2751] Make some minor comment updates

src/lib/datasrc/memory/rdataset.h

@@ -229,7 +229,8 @@ public:
     /// even when subtracting data from the old_rdataset, since a new
     /// copy is being created.
     ///
-    /// The old_rdataset is not destroyed and it is up to the caller.
+    /// The old_rdataset is not destroyed and it is up to the caller to
+    /// manage its allocation.
     ///
     /// \throw util::MemorySegmentGrown The memory segment has grown, possibly
     ///     relocating data.
@@ -239,8 +240,8 @@ public:
     /// \param mem_sgmt A \c MemorySegment from which memory for the new
     /// \c RdataSet is allocated.
     /// \param encoder The RDATA encoder to encode \c rrset and \c sig_rrset
-    /// with the \c RdataSet to be created.
-    /// \param rrset A (non RRSIG) RRset containing the RDATA that are not
+    /// with the \c RdataSet is to be created.
+    /// \param rrset A (non-RRSIG) RRset containing the RDATA that are not
     /// to be present in the result. Can be NULL if sig_rrset is not.
     /// \param sig_rrset An RRSIG RRset containing the RRSIGs that are not
     /// to be present in the result. Can be NULL if rrset is not.

src/lib/datasrc/tests/memory/rdataset_unittest.cc

@@ -269,7 +269,7 @@ TEST_F(RdataSetTest, subtract) {
             holder1.set(RdataSet::create(mem_sgmt_, encoder_,
                                  (i & 1) ? a_rrsets : null_rrset,
                                  (i & 2) ? rrsig_rrsets : null_rrset));
-            // Create merged rdataset, based on the old one and RRsets
+            // Create subtracted rdataset, from the old one and RRsets
             SegmentObjectHolder<RdataSet, RRClass> holder2(mem_sgmt_, rrclass);
             holder2.set(RdataSet::subtract(mem_sgmt_, encoder_,
                                  (j & 1) ? a_rrsets_rm : null_rrset,