Matthew Wilcox and others have been working on allowing the EXT4 file-system to optimally use NVDIMM DRAM when it's treated as a block device. Currently the usage of EXT4 on NVDIMMs is sub-optimal, as explained by Wilcox, "One of the primary uses for NV-DIMMs is to expose them as a block device and use a filesystem to store files on the NV-DIMM. While that works, it currently wastes memory and CPU time buffering the files in the page cache. We have support in ext2 for bypassing the page cache, but it has some races which are unfixable in the current design. This series of patches rewrite the underlying support, and add support for direct access to ext4."
This direct access support for EXT4 and ported from the EXT2 implementation should significantly help out the popular Linux file-system when using NVDIMMs; the direct access (DAX) mode basically avoids double-buffering data before copying it to the device. While these patches are up to revision eight, they haven't yet been pulled into the EXT4 tree for merging into the mainline kernel, but for now can be found via the Linux kernel mailing list.