Since kernel-genkernel-x86-2.6.29-gentoo-r1 and aufs 20090126 (thats aufs1) there is a very strange effect with pdflush.
After some minutes pdflush gets very busy and the system becomes unuseable. This only appears when using an ext3/4 overlay in aufs.
I still got this problem with 2.6.29-r3 and aufs2 while the vanilla sources (184.108.40.206) work perfect.
Steps to Reproduce:
1. build an aufs-root and start gentoo in it (i did this via a custom initrd)
2. also add an additional ext3 or ext4 partition to the aufs branch (my setup is squashfs+ext3/4+tmpfs)
3. XESSION=fluxbox startx
Just wait some minutes (2-8) and pdflush suddenly becomes very busy. Even killing X does not calm down pdflush again.
Normal behavior and a low system load.
I suppose it's cos of the ext- patches in the gentoo-sources . So probably the best way to test is, applying every patch step by step, recompile the kernel and check whenever the problem occurs again.
I have similar problems on gentoo-sources 2.6.28 and 2.6.29, but also on vanilla-sources 2.6.29 and 2.6.30_rc7. For me pdflush gets busy when I had open login on virtual console and from KDE I try to Reboot/Poweroff. There's a window pop-up that asks if I want to terminate active sessions and at the same moment pdflush goes nuts. After that I cannot unmount or sync root partition (ext4), but other partitions(some ext4 and reiserfs) seem to be unaffected. Maybe it's just because there aren't any open files on other partitions but it's just a guess.
Sorry, we can't support kernels that have been modified with out-of-tree components. Also aufs1 doesn't seem to even be a gentoo package so I can't reassign to its maintainer.