[PATCH 00/12] radix-tree: split out struct radix_tree_root out to <linux/radix-tree-root.h>

[Matthew Wilcox]

On Mon, Oct 09, 2017 at 01:10:01AM +0900, Masahiro Yamada wrote:
> Reducing the header dependency will help for speeding the kernel
> build, suppressing unnecessary recompile of objects during
> git-bisect'ing, etc.

Well, does it?  You could provide measurements showing before/after
time to compile, or time to recompile after touching a header file that
is included by radix-tree.h and not by radix-tree-root.h.

Look at the files included (never mind the transitively included files):

#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/spinlock.h>
#include <linux/types.h>

These are not exactly rare files to be included.  My guess is that most
of the files in the kernel end up depending on these files *anyway*, either
directly or through some path that isn't the radix tree.