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Date:   Mon, 18 Feb 2019 20:28:44 -0800
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Networking <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        atish patra <atishp04@gmail.com>,
        Daniel Colascione <dancol@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Karim Yaghmour <karim.yaghmour@opersys.com>,
        Kees Cook <keescook@chromium.org>, kernel-team@android.com,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Manoj Rao <linux@manojrajarao.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Yonghong Song <yhs@fb.com>
Subject: Re: [PATCH v2 1/2] Provide in-kernel headers for making it easy to
 extend the kernel
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On Tue, Feb 19, 2019 at 01:14:11PM +0900, Masahiro Yamada wrote:
> 
> I was able to compile it in-tree
> but it makes the incremental build extremely slow.
> 
> (Here, the incremental build means
> "make" without changing any code after the full build.)
> 
> Before this patch, "make -j8" took 11 sec on my machine.
> 
> After this patch, x86_64_defconfig + CONFIG_IKHEADERS_PROC=y
> takes 53 sec for me since kernel/kheaders_data.txz is regenerated
> every time even when you did not touch any source file.
> 
> We should take time for careful review and test.
> 
> Please give me more time for thorough review.

Thanks for taking a look. All are very valid points.
Incremental build is must have.