OOM when add new node to replica set

We meet a OOM problem when we add a new node(with 16GB memory) to replica set , there are about 200GB data on primary node , it takes 1 hours before OOM . We have tried some times, but same result.

"top" command has been run on our linux system there are almost no buffer,Cache,Free memory before OOM.

We notice there are much "building index using bulk method; build may temporarily use up to 500 megabytes of RAM" in log. We found a parameter named "secondaryIndexPrefetch" to release resource for building index , but it doesn't work in WT.