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References: <20220228071022.26143-1-songmuchun@bytedance.com>
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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Mon, 28 Feb 2022 23:14:27 +0800
Message-ID: <CAMZfGtXvLj+DQj=YoN6CcVfHZA-ceB24t8waMZs7KEbOoh0jUA@mail.gmail.com>
Subject: Re: [PATCH 3/3] mm: hugetlb: add hugetlb_free_vmemmap sysctl
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Xiongchun duan <duanxiongchun@bytedance.com>
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On Mon, Feb 28, 2022 at 10:42 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> On Mon, Feb 28, 2022 at 03:10:22PM +0800, Muchun Song wrote:
> > We must add "hugetlb_free_vmemmap=on" to boot cmdline and reboot the
> > server to enable the feature of freeing vmemmap pages of HugeTLB
> > pages. Rebooting usually taske a long time. Add a sysctl to enable
> > the feature at runtime and do not need to reboot.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  Documentation/admin-guide/sysctl/vm.rst | 13 +++++++++++++
> >  include/linux/hugetlb.h                 |  5 +++++
> >  include/linux/memory_hotplug.h          |  1 +
> >  kernel/sysctl.c                         | 11 +++++++++++
>
> kernel/sysctl.c is a hot mess with tons of knobs from all over the
> place. And so we've been moving these to their own place. For instance
> all the filesystem knobs are now properly in fs/. So Adding new ones
> to the file is undesirable. If this is going to be added, please add
> it somewhere in mm / hugetlb code.
>

I also have realized this when reading another patch [1]. I will
move this into its hugetlb related code.  Anyway, thanks for
your suggestion.

[1] https://lore.kernel.org/linux-fsdevel/20220220060626.15885-1-tangmeng@uniontech.com/