android build time become slow when using unionfs/aufs
===

I download android 4.1.1_r1 and like to use unionfs* like fs to keep source code clean.
However, I fount that the make time become slow when using it,
Is any suggestion that I can improve the build time?

Thanks

Below are my steps:
######## Normal build ######

    $ source build/envsetup.sh
    $ lunch full-eng
    $ time make -j16
    real    14m35.194s

###### unionfs fuse ########

    $ sudo apt-get install unionfs-fuse
    $ unionfs-fuse temp=RW:android-4.1.1_r1=RO build
    $ cd build/
    $ source build/envsetup.sh
    $ lunch full-eng
    $ time make -j16
    real    22m37.899s
    
    $ cd ..
    $ fusermount -u build

####### Aufs ###############

    $ mkdir temp build
    $ sudo mount -t aufs -o br=temp=rw:android-4.1.1_r1=ro none build
    $ cd build
    $ source build/envsetup.sh
    $ lunch full-eng
    $ time make -j16
    real    16m9.366s
    
    $ cd .. && sudo umount build

