(Eu tenho exatamente o mesmo problema.) A única informação que pude encontrar sobre isso é:
De link :
Maybe it wasn't clear, but the number of lower layers isn't limited by
FILESYSTEM_MAX_STACK_DEPTH, only by the max size of the mount option buffer in
the kernel (1 page, usually 4096bytes). So you could have a hundred read-only
layers stacked in a single overlayfs mount.
As for changing the stacking while the overlayfs is mounted: currently this is
not supported, the layers specified at the mount time remain there until the
overlay is unmounted. Currently there's no possibility to add or remove layers
in a dynamic way, and it is definitely more tricky to implement than the static
configuration.
-- Miklos Szeredi Mon, 10 Nov 2014