I applied your patch to the vanilla 184.108.40.206, enabled everything and added "zcache" to my kernel parameters. But after rebooting, statistics in /sys/kernel/mm/ show that neither cleancache nor frontswap are ever used. /sys/kernel/mm/zcache is not even there. Is there anything missing from the vanilla kernel that frontswap, cleancache or zcache require?
I tried zcache both in-kernel and as a module.
And now that zcache is included in 2.6.39, are there patches for frontswap and cleancache that can be applied to that kernel? I tried the latest ones from lkml but some hunks failed. I then tried to apply them manually but ran into trouble in swapfile.c.