Re: [PATCH V2 4/4] LoongArch: Enable ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

From: Feiyang Chen <chris.chenfeiyang@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Huacai Chen <chenhuacai@loongson.cn>,
	Huacai Chen <chenhuacai@kernel.org>,
	 Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	 Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	loongarch@lists.linux.dev,
	 linux-arch <linux-arch@vger.kernel.org>,
	Xuefeng Li <lixuefeng@loongson.cn>,  Guo Ren <guoren@kernel.org>,
	Xuerui Wang <kernel@xen0n.name>,
	 Jiaxun Yang <jiaxun.yang@flygoat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Linux-MM <linux-mm@kvack.org>,
	 "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Feiyang Chen <chenfeiyang@loongson.cn>
Subject: Re: [PATCH V2 4/4] LoongArch: Enable ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
Date: Thu, 30 Jun 2022 14:55:54 +0800	[thread overview]
Message-ID: <CACWXhKn9FEWMc_QkrPsXUxTP33BnzZCZuesxNRDYaAWnSxWtsA@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1x=ZX+W0XL-=MkZebHdbvB0Ngam5LxXJUnm7USpMaFMA@mail.gmail.com>

On Thu, 30 Jun 2022 at 14:07, Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Thu, Jun 30, 2022 at 6:32 AM Huacai Chen <chenhuacai@loongson.cn> wrote:
> >
> > To avoid build error on LoongArch we should include linux/static_key.h
> > in page-flags.h.
>
> This is an expensive change in terms of compile speed, as static_key.h has
> lots of dependencies, and page-flags.h is included in a lot of places. What
> it is actually needed for?
>

Hi, Arnd,

If CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP=y, the page-flags.h relies
on static keys. If we don't include static_key.h, we will get the
following errors when compiling.

In file included from ./include/linux/mmzone.h:22,
from ./include/linux/gfp.h:6,
from ./include/linux/mm.h:7,
from arch/loongarch/kernel/asm-offsets.c:9:
./include/linux/page-flags.h:208:1: warning: data definition has no
type or storage class
208 | DECLARE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
| ^~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/page-flags.h:208:1: error: type defaults to 'int' in
declaration of 'DECLARE_STATIC_KEY_MAYBE' [-Werror=implicit-int]
./include/linux/page-flags.h:209:26: warning: parameter names (without
types) in function declaration
209 | hugetlb_optimize_vmemmap_key);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/page-flags.h: In function 'hugetlb_optimize_vmemmap_enabled':
./include/linux/page-flags.h:213:16: error: implicit declaration of
function 'static_branch_maybe' [-Werror=implicit-function-declaration]
213 | return static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
| ^~~~~~~~~~~~~~~~~~~
./include/linux/page-flags.h:213:36: error:
'CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON' undeclared (first
use in this function); did you mean
'CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP'?
213 | return static_branch_maybe(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
./include/linux/page-flags.h:213:36: note: each undeclared identifier
is reported only once for each function it appears in
./include/linux/page-flags.h:214:37: error:
'hugetlb_optimize_vmemmap_key' undeclared (first use in this
function); did you mean 'hugetlb_optimize_vmemmap_enabled'?
214 | &hugetlb_optimize_vmemmap_key);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
| hugetlb_optimize_vmemmap_enabled

Thanks,
Feiyang

>          Arnd
>