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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Tue, 5 Jul 2022 15:51:06 +0800
Message-ID: <CAMZfGtXLxPO3jmkKpF7n9Scb=542yrf1taWHZGdPwK-tZsJXgQ@mail.gmail.com>
Subject: Re: [PATCH V4 4/4] LoongArch: Enable ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
To:     Huacai Chen <chenhuacai@kernel.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Huacai Chen <chenhuacai@loongson.cn>,
        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>
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On Tue, Jul 5, 2022 at 2:22 PM Huacai Chen <chenhuacai@kernel.org> wrote:
>
> Hi, Arnd,
>
> On Mon, Jul 4, 2022 at 8:18 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Mon, Jul 4, 2022 at 1:25 PM Huacai Chen <chenhuacai@loongson.cn> wrote:
> > > To avoid the following build error on LoongArch we should include linux/
> > > static_key.h in page-flags.h.
> > >
> > > 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
> >
> > I wonder if page_fixed_fake_head() should be moved out of line to avoid
> > this, it's already nontrivial here, and that would avoid the static key
> > in a central header.
> I have some consideration here. I think both inline function and
> static key are instruments to make things faster, in other words,
> page_fixed_fake_head() is a performance critical function. If so, it
> is not suitable to move it out of line.

+1

The static key is an optimization when HVO is disabled.

Thanks.

>
> Huacai
> >
> >        Arnd
> >