does not use existing css cache
mkdir() followed by checking errno for EEXIST is not sufficient to determine if a directory exists. Using Ubuntu 16.04.1 with the cache dir on an nfs filesystem, mkdir() is returning EACCESS when the directory exists, with the result that the cache is not used. See https://lkml.org/lkml/2016/7/8/814
The easy fix is to wrap mkdir - patch attached. The better fix might be not to use mkdir this way at all. Just try to open the cache and if it's not found try to create it. That would be a bigger change but if there's interest I might try to write such a patch.