No. it is not possible to configure the cache size for MMAPv1 because MMAPv1 does not allow configuring the cache size.

In MongoDB, MMAPv1 is a storage engine that uses memory-mapped files for data storage. As of my last knowledge update in January 2022, MMAPv1 does not have a specific cache size configuration like the WiredTiger storage engine, which replaced MMAPv1 as the default storage engine starting from MongoDB version 3.2.

WiredTiger has a configuration option called storage.wiredTiger.engineConfig.cacheSizeGB that allows you to set the cache size. However, for MMAPv1, the cache size is generally determined by the operating system’s virtual memory manager, and MongoDB doesn’t provide a direct configuration option for it.

If you are using a version of MongoDB that still supports MMAPv1, please refer to the MongoDB documentation specific to that version for the most accurate and up-to-date information. Keep in mind that MongoDB is actively developed, and features and configurations may change with newer releases.