Comment 4 for bug 1311987

This turns out to be a kernel issue, either upstream or in Ubuntu. Bisected to the following, which was released in 3.12.

commit 16203a7a9422315bc929461503e3a046459ea5ff
Author: Rob Landley <email address hidden>
Date: Wed Sep 11 14:26:12 2013 -0700

    initmpfs: make rootfs use tmpfs when CONFIG_TMPFS enabled

    Conditionally call the appropriate fs_init function and fill_super
    functions. Add a use once guard to shmem_init() to simply succeed on a
    second call.

    (Note that IS_ENABLED() is a compile time constant so dead code
    elimination removes unused function calls when CONFIG_TMPFS is disabled.)

I agree this is an edge case for tripleO but not so much for general Ironic usage, as admins should be free to declare nodes with as little memory as they want, and DIB produced deploy-ironic ramdisks should be expected to work.