hmh:

The config help for CONFIG_PROCD_ZRAM_TMPFS is missing several dependencies, without which the feature will fail to work at runtime.

On LEDE-17.01, one must set:

CONFIG_PROCD_ZRAM_TMPFS=y
CONFIG_PACKAGE_kmod-zram=y
CONFIG_PACKAGE_kmod-fs-ext4=y
CONFIG_PACKAGE_e2fsprogs=y

as well as their dependencies, for the "use zram for /tmp" feature of procd to work.

Either CONFIG_PROCD_ZRAM_TMPFS needs to arrange for these dependencies to be force-enabled, or its help text needs to document the need for them. The ext4 ones are anything but obvious...

Apparently, this issue is still present in openwrt-18.06 and trunk.