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Date:   Mon, 28 Feb 2022 06:41:59 -0800
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     corbet@lwn.net, mike.kravetz@oracle.com, akpm@linux-foundation.org,
        keescook@chromium.org, yzaikin@google.com,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, duanxiongchun@bytedance.com
Subject: Re: [PATCH 3/3] mm: hugetlb: add hugetlb_free_vmemmap sysctl
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References: <20220228071022.26143-1-songmuchun@bytedance.com>
 <20220228071022.26143-4-songmuchun@bytedance.com>
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Sender: Luis Chamberlain <mcgrof@infradead.org>
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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.

  Luis