linux-kernel - Re: [PATCH 00/12] radix-tree: split out struct radix_tree

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Date:   Tue, 10 Oct 2017 05:18:30 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ian Abbott <abbotti@....co.uk>, Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-cachefs@...hat.com, linux-sh@...r.kernel.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        linux-rdma@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Tariq Toukan <tariqt@...lanox.com>,
        Rich Felker <dalias@...c.org>,
        Leon Romanovsky <leonro@...lanox.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        David Howells <dhowells@...hat.com>,
        intel-gfx@...ts.freedesktop.org,
        Yishai Hadas <yishaih@...lanox.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Matan Barak <matanb@...lanox.com>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        linux-fsdevel@...r.kernel.org, Marc Zyngier <marc.zyngier@....com>
Subject: Re: [PATCH 00/12] radix-tree: split out struct radix_tree_root out
 to <linux/radix-tree-root.h>

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.