[PATCH 0/6] Shrinking DT memory usage

From: Rob Herring
Date: Thu Oct 05 2017 - 15:44:32 EST

On kernels with a minimal config and a RAM target in the 100s of KB, DT
is quite a hog of runtime memory usage. How much is dependent on how many
nodes and properties in the DT which have a corresponding struct device_node
and struct property in the kernel. Just skipping disabled nodes saves a
lot by not creating the device_nodes in the first place[1], but there's
more low hanging fruit by making some of the fields in struct property and
struct device_node optional. With the changes here, the memory usage goes
from 17KB to under 8KB on QEMU's ARM virt machine which is a relatively
small DT.

The majority of the diffstat here is just moving all the kobject/sysfs
related code to its own file so we can avoid adding a bunch of ifdefs.

There's more drastic approaches we could take such as doing the
unflattening at build time and storing the bulk of the unflattened tree
as const data. Grant also has some ideas on storing properties as ids
instead. He's explained it to me, but I still don't understand it.


[1] https://patchwork.kernel.org/patch/9983203/

Rob Herring (6):
of: fix missing kobject init for !SYSFS && OF_DYNAMIC config
of: remove struct property.unique_id for FDT
of: make struct property _flags field configurable
of: move kobj_to_device_node() into dynamic.c
of: wrap accesses to device_node kobject
of: make kobject and bin_attribute support configurable

drivers/base/core.c | 2 +-
drivers/of/Kconfig | 4 ++
drivers/of/Makefile | 1 +
drivers/of/base.c | 133 ---------------------------------------
drivers/of/dynamic.c | 27 ++------
drivers/of/kobj.c | 164 ++++++++++++++++++++++++++++++++++++++++++++++++
drivers/of/of_private.h | 29 +++++++--
include/linux/of.h | 28 +++++----
8 files changed, 215 insertions(+), 173 deletions(-)
create mode 100644 drivers/of/kobj.c