Meta mode is an incremental build option for FreeBSD, which uses bmake's meta mode and filemon(4) to create meta files. It substantially decreases the time it takes to build FreeBSD, by only building what has changed since the last build.
You also need to make cleanworld once. If objects don't have .meta files then META_MODE won't do the right thing on an incremental build. (Source: [CFT] WITH_META_MODE: Working incremental build)
Now you can follow the handbook and you should be fine.
Don't mix WITH_META_MODE with ccache(1) as mentioned in this thread .
- Actually, I'm happily using both technologies on 12.0-CURRENT without any problems.
WITH_META_MODE is not the same thing as WITH_DIRDEPS_BUILD, which is an alternative, experimental build system.