Tobias Wilken:
> Hey, you are the best.

Agreed. :-)


> My `while(true); do ls -al; done` leads to great result. Now I have to

Glad to hear that.


> Two thoughts about the solution:
>  - Do you have an idea about the performance advantage of the cache or
> performance lost?

The rdcache=0 option makes the aufs readdir cache unusable, but the
cache itself still exists. It is definelty the waste of memory.
So I'd suggest you to try RDU (readdir in userspace).
- get the latest aufs source files with aufs2-util.
- enable CONFIG_AUFS_RDU.
- install the kernel or aufs module.
- reboot.
- build aufs2-util and "make install_ulib", which installs
  /usr/lib/libau.so.
- set the environment variables LD_RELOAD=libau.so and LIBAU=readdir.
- if you want, write these variables in your /etc/environment or
  something in order to make them system-wide.
- read the aufs manual about RDU in detail.

By RDU, you can make the size of the aufs readdir cache zero. It must be
the best at the memory performance. Regarding to the speed performance,
generally (as far as I know) RDU runs faster than normal aufs
readdir. RDU runs in userspace mostly and I think it is better to the
entire system too.


>  - What's about setting udba to none in this case?

Generally udba=reval is the best I believe.
As long as all of your lower readonly branch is never be changed and
your upper writable branch is fuse, by disabling CONFIG_AUFS_HINOTIFY
and speciry udba=none option you will get better performance I guess.


J. R. Okajima

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