I know this is a known and solved problem with CONFIG_ZCACHE=m I hit a while back:

  Building modules, stage 2.
  MODPOST 258 modules
ERROR: "xv_malloc" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_new_pool" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_put" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_destroy_pool" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "xv_free" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "xv_get_object_size" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_get" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_flush_object" [drivers/staging/zcache/zcache.ko] undefined!
ERROR: "tmem_flush_page" [drivers/staging/zcache/zcache.ko] undefined!

The patch for this isn't in the linux-next tree I pulled yesterday - what happened to it?