VMsep (VM-separated commit on jbd2/ext4)

• Nested ext4 filesystems on both guest and host machine can incur excessively frequent journal commits.
• VMsep can dramatically reduce write traffic by managing modified file blocks from each guest as a separate list and splitting the running transaction list into two sub-transactions.
• Filebench and IOzone benchmarks show that VMsep improves the I/O throughput by 19.5% on average and up to 64.2% over existing systems.

Build

• VMsep source came from linux 4.13.0-45
• adjust include/{linux,trace} pointing to VMsep's include
• just make
• After build done, you have two kernel modules in kernel/fs/{jbd2/jbd2_vmsep.ko,ext4/ext4_vmsep.ko}